Help, bad thermostat??

[Nephil]

I keep getting issues and it's exhausting to stress for each one of them. After 2-3 months of no issuess w temp i saw that the cool side keeps overheating to 29°(C). I use a probed thermometer and 2 heat mats to warm up my BP's container and each is attached to a thermostat. I noticed that the cool side just suddenly started to have problems, and before i set my thermostat to warm up till 26°,but after seeing the high temps i switched to 25°, with no change. The thermostat still always shows 26°, it stays like that for a while, and then it lowers but if it ends up under 25° it turns the power on and the temp rockets to 29° (on my thermometer) then after the stat reached "26°" everything seems to cool down bit by bit, but then it overheats again and it goes on like a roller-coaster. What the hell is happening?? I also want to clear out that it's probably not my thermometer's problem, cause even though the thermostat says it's 26° the ground feels very warm, warming up hides and just anything in the enclosure. I also want to add that my thermostat reads temp slower than the thermometer.