Air carrier flight crew reported receiving ECAM message regarding IDG overheat during taxi for takeoff. Flight crew returned to the gate.

Narrative

Holding short of Runway XX just prior to takeoff we received an ECAM Caution Message 'IDG 1 OIL OVERHEAT' and instructions to disconnect the IDG. While the Captain (CA) and I discussed disconnecting the IDG versus shutting the #1 engine down; the ECAM popped up with 'IDG 2 OIL OVERHEAT.' Having two completely independent systems show the same fault was highly unusual and we suspected a sensor or computer malfunction; but we honored the messages by starting the APU and shutting down the engines; and requested Airport Rescue and Firefighting (ARFF) to examine the aircraft as well as measure the temperature of the engines. Somewhere during the event prior to shutting down engines; I believe I saw an incredibly brief Eng Fire indication for Engine #2; but the Master Caution and ECAM display were so fast I cannot confirm that is what I saw. I have doubts about what I did see. While we waited; we examined our manuals (AOM; ASM; QRH) without any particular information given to our situation. Researching on the internet I learned about when the IDG overheat advisory and cautions pop up (142 and 185°C respectively). Checking the ELEC page I saw 174°C on the #2 IDG and 158°C on IDG #1. Both were flashing and cooled very slowly over the next hour or so. After reporting all our information to maintenance personnel back at the gate; they performed an inspection of both IDGs. They showed me the IDG #1 Oil gauge. The 'full' line marking was in the middle of the window but the window was filled all the way to the very top and the color of the liquid was red. We remained in contact with the maintenance personnel via cell phone text messages and the next day they confirmed both IDGs had been completely over serviced and with the wrong type of oil. Had we taken off and immediately had this issue; we would have quickly been on battery power only; flying through the weather in extremely mountainous terrain.Whoever serviced the IDGs with too much oil and the wrong type caused this problem.Maintenance personnel must follow correct procedures when performing work on our aircraft. This event needs closer inspection to understand how this happened and whether other measures must be taken to ensure procedures are followed.