Lake of knowledge and unprofessionalism

I had the worst experience ever with sheet street, I opened an account with them and in a few months there was ***** committed on my account and it took them more than six months to resolve the issue but I kept paying my part of the balance but now they failed to reverse the interest that was charged because of the highest balance and they failed to adjust the installment that was calculated on a high balance, now my name is listed on itc because of them and trying to talk to them is a nightmare and they have the audacity to say my account is in arrears, I want them to deal with this and sort out their mess, I deal with ***** in the same industry and I know exactly how to resolve such issues, their call center seems to be unequipped to deal with such issues, how do you take more than six months to resolve *****, I just want them to sort this out and remove my name from the itc