WELLS FARGO CHARGED ME $700 INTEREST ON $90 FEE

I opened an 18 month no interest payment plan with Wells Fargo when I got eye surgery. Everything went smoothly and for 17 months I had been paying it off. The last month - January -, I never received a statement (I had about $90 left to pay off of $3000), but I received a $600 statement in February. I called to inquire about it and I was told the account is paid off and I can just ignore it. I kept receiving higher and higher amounts every month so I called again in May. I was told there is one more payment of $98 and because it wasn't made in time I am now charged interest on the entire amount. I tried to explain that I never received a statement to no avail. I called again in June and I was told they have no record of me calling them, on the contrary they called me a year and a half before and that is the last time we had been in contact. Of course, they also stated they refuse to waive any fees. I asked to speak to a manager, and after I was on hold about 10 minutes, a manager came on the line who clearly knew what was going on from the customer service department. He was rude and told me billing statements are a COURTESY, I should know what my balance is and pay it off. He also told me they have no record of me calling in and I must have been calling the wrong number.