Bad service from account department

I had a contract with Mtn since 2008/2009 which was so happy with their service up until 2017, I paid my contract via Eft using my *** as a reference and my sim was blocked due to non payment went to Mtn William Moffett with the proof and phoned the customer my no will be unblocked for 2 days then back to square 1, I even forwarded the proof of payments to Mtn accounts up until now the sim card is blocked still waiting for feedback from them instead they handed over my account to Debt collectors. I still have copies of communication I sent to Mtn my contact ***