Unallocated payments and poor service

Good day,

I have an fnb account handed over to nimble group, I have bee paying for the account but none of the payments reflect on the statement they sent me. I raised this with them in December 2017 and also sent them the proof of payments but still not allocated. been communicating with their sarcastic, inefficient consultant Joshua Dondolo who indicated that he has done all he could possibly do with the matter and there is nothing else he can do. their head office in cape town claims that I have to take this up with FNB which I don't understand as they furnished me with their banking details, not FNB.This has resulted in the account accruing interest monthly. I need the payments allocated and to be advised of the balance remaining. I have been emailing Joshua and Sibongile but hardly get any feedback.