Ungoverned Call Centre, Unmanageable Managers

My Woolworths Credit card account was handed over to MBD because of errors i had incurred. Since then there is an agreement to pay R350 per month via debit order which i am honouring. In 2018 Nov/Dec i deposited an amount of R2120 into their account to reduce what i was owing. Since then i have been making followups as to whether they got the amount or not since there was no acknowledgement. They told me it would take a bit longer to appear since it was a cash deposit. They asked me to email the proof of payment to ********** and i did but to this day they cannot trace it. I kept making follow ups that i ended up talking to one the managers Cheron who promised to take the matter up and get back to me. Now everyone is giving me the run around. I want to settle my debt but i cannot do so until the money is tracked and deducted from my balance. I am now frustrated because no one is assisting me, they keep droping my calls and promising to call me back. Please assist