Frustrated customer

I am financed by MFC part of Nedbank group.. I am unemployed (retrenched) and have fallen behind with my car repayments to which there was an agreement with their legal department to pay a certain lumpsum, continue to pay normal installments, then top up with additional amount to cover the arrears. This was done telephonically to which I wrote an email to the MFC legal dept gentleman as a record of the telephone agreement. I have been honoring the agreement. I am shocked when they send a guy to collect thenas I am making my payments. Each time they send a guy to collect when I call the MFC gentlemen he always tells me that he will take the matter to his manager and come back to me and he never does. They have send three collection companies thus far and everytime I send proof of the arrangement and proof of payment then the collection guy backs off. Then a guy will be send again then same story. I have been asking the gentlemen for the audio recording of the agreement and he told me he doesn't know how to retrieve it and will ask his manager. I am living in fear of my car been taken while I am honering the payment agreement but the bank still sends these collection guys after me. I don't know what to do anymore as no senior person is willing to talk to me. I desperately need help.