Air Carrier First Officer describes the process of calling in fatigued after an early reserve assignment is changed in the middle of the night; by scheduling; to a late trip assignment.

Narrative

I am a reserve FO out of ZZZ1. I was assigned early reserve for four consecutive days in June. It is reasonable to believe I will be called to fly as early as XA00 in ZZZ1 because the trips begin very early. Even if assigned to another base's trips; there is a good chance you are on the first flight out in the morning to get you in position at a hub. I went to bed at XS00 local time in ZZZ1 so that I would be well rested for a XS00 wakeup call. I was called at XS06am on JUNE 09. The scheduling coordinator said that I was going to be put back on rest; and I would have a XL15 show now; and would DH to ZZZ; sit for 3+ hours; then fly to ZZZ2 after that and arrive in ROC around XS30. That is a really long day for me; I explained. MR. X said 'no you're back on rest it is a legal rest assignment and flying assignment.' I explained that I have already slept; now I'm awake; how can I be expected to sleep even longer? and through the daylight? I was met with no remorse and told it was a 'legal assignment;' again. It may be legal on paper I said; but I am not a robot. I explained that around XO00-XP00pm I will be pretty tired based on being up at XA00AM. That is the maximum time that I would be working had I never been put on rest. We both hung up. I was also stuck between a rock and a hard place. I knew I would not be fit for flight at that time of day; however I could not call in fatigued or not accept the trip because it would be classified as 'refusing the trip;' and I would get in trouble for doing that! Around XK30PM; I called scheduling back and talked to the same scheduler again. I told him as I predicted I was unable to fall asleep and if this day continues the way it is; I will be too tired to fly to ZZZ2 tonight. Again; no remorse. I finally decided to call in fatigued at XP00 EST. After being up for over 15 hours. The flight was not for another 2 hours; and then a 1.5 hour flight after that. I did not believe that I would be able to perform my duties as a flight crew member safely being up for so long. When I called in fatigued; the first words out of the schedulers mouth was 'It's a legal assignment.' I had never even said why I was calling in fatigued. At this point; I was met with several other aggressive questions about my status. I felt as if it they were telling me it was not ok to call in fatigued even though; I knew I was. The scheduler was very unhappy; and even hung up the phone on me without even closure of the situation from my standpoint. I was in ZZZ now; but without a hotel room. I had to call back and ask for one. Their response; 'Ya; we'll get to that when we have time; we're busy with other things right now.' At this point; I felt as if I was being punished for calling in Fatigued. The whole process of calling scheduling and telling them this was the hardest part of my day. I was pressured; and then shamed for calling in fatigued. I ended up getting a room at the hotel near the airport; but with no call from scheduling. I knew we stayed there; so I went there to see if they had a room for me. They did.There is a serious pilot shortage here. There are very few reserve pilots to fly more than a full schedule of work. Every reserve day of my schedule is often covered with a reserve assignments. These assignments are not as productive as a line holders assignments. Often 8+ hours of sitting in an airport; and 14+ hour duty days and 16+ awake hours. There are no 'PM' reserves in ZZZ1 scheduled in advanced because the majority of trips begin early. However; if a trip does come up at the end of the day; PM reserves only come about as a result of a previous trip. For example; a 3 day trip that ends late; and the pilots has 4 days of reserve. Day 4 would be late reserve. AM reserves can be put back on 'rest' and forced to fly a PM trip. If a pilot does not like this; the only thing he could do is wait until the trip starts to call in fatigued; when it is obvious that he was not going to be to be able to fly. Acting before this; scheduling says that the pilot is 'refusing the trip;' which reflects badly on the pilot - which is not the case at all. Scheduling should not TRY to be the boss of the pilots. However inconvenient a fatigue/sick call is; they seem to take it personally. My experience is very negative; in a way that I felt almost pressured to not call in fatigued. I don't believe this is how I should feel.