Money missing, interest rates double!!

We signed up a good few years ago, and going through my statement with one of my accounts it did not make sense as it should have been paid off by now. Only to notice that the negotiated interest according to them of 8.25% is actually double of 15%, there are payments that have been made to them and have NOT been paid into this account - so where is that money? I have sent several emails, only to be ignored. Your service is pathetic, lock down or not, this is a person's hard earn money you are messing with and you are quick to take your fees.