Reversal of unpaid fees

I placed a stop payment on a debit order as i am making internet payments into my loan account . It still goes through every month , and i am being charged unpaid charges . I have to query this every month spending ample of time on the phone. For the first few months the charges were reversed .Suddently when i queried it in Sept , i was told that a stop payment cannot be put on a loan account and the fees cannot be reversed .My question is why did the system accept the stop payment .I stopped the payment as there is no funds going into that account . I requested the call centre to cancell the debit order , of which was also not done .Meantime , they are ripping me off with unpaid charges.A debit order went though my account in Sept , of which i gave no authorisation for.It did not even reflect on my statement , but i was charged unpaid charges.I queried it and was told it is from NKS DBN, of which i have no dealings with, i am still waiting on feedback . I sent several e-mails to the complaints department , but had no joy . Leroy called me a while back and gave me an explanation that make no sense . My account is in overdraft due to these charges and i keep getting reminders .