A Flight Attendant reported the flight returned to departure airport due to an engine malfunction.

Narrative

Upon checking in at airport we had a gate change from X to Y. Our original gate was now going to ZZZ. So we proceeded to our new gate and prepared for our flight. After take off and reaching; cruising altitude; Flight Attendant (FA) A and I got up to start setting up for the service. Shortly after the captain called and gave information to FA B and FA C. He said here is your briefing information. There is a malfunction to the left engine and we will be landing in 20 minutes. He asked for FA B to check and view the left engine from the window. So we closed up the galley and prepared the cabin for landing and instructed the passengers in row seven and eight window seats to keep an eye on the left engine and ring their call button if they saw anything . We also instructed the exit row on the left side as well. We landed pretty hard and with pumped hard breaking; and I could see all the vehicles coming fast toward our airplane from my jumpseat. After it was safe to do so; we parked at the gate and deplaned the passengers . We then had an in-flight supervisor come and debrief with us and then we debriefed with the pilots. The captain had advised us that the left engine had been written up prior to our flight for a problem with an overheating left engine. And the detection was for fire in engine but didn't say that up in the air. We then went to our in-flight office to meet with a supervisor to tell them what happened and they released us for the day with pay. We were all pretty distraught and just wanted to go home. My questions are -If the planes engine had been written up for overheating why was it deferred and the plane in service? Was our plane refused by the previous pilots that were now at our original gate to ZZZ? Why were we not instructed to prep the cabin for evacuation? If there were all the vehicles ready in case - we should have also been ready to evacuate. If we were landing heavy with fuel and a possible fire in engine it could have been a disaster.