I just went through the same thing. I have a 500 gallon propane tank I am paying "rental" on. I haven't filled it for a couple years, since I use the furnace very little. So,,,,,,,,,,, I continued to pay the rental fee until it was almost empty, and just purchased a 100 # tank for my cooking stove. You just have to look at where you can get the most bang for your buck. If you fill it more now to avoid the $125 fee,,, will it just snowball next year?? Then you will have more in the tank, and another $125 bill??
Might be better off to have them empty it, and take the refund on propane now, and cut your losses.