Threatened by MFC staff members

I bought a new vehicle in 2008 with a balloon payment.. On the 18th of the 5th I received an e-mail from MFC with the new re-financed structure which Included the period and amount that I had to pay. I inquired as to the Interest rate and they informed me that I am paying 17%. I inquired as to why and they said, it is what it is! I signed the document with the period and amount marked with an X next to the options.The period I agreed upon was for 36 months at R 1 123.00 per month and I actually paid R 1 200.00 per month. Two months later I started to receive phone calls from a collections agency informing me that my account is in arrears and that I must pay immediately, I forwarded them the agreement and it was quiet. Yesterday the collections agent phoned me again, this time telling me that if I do not pay they will come and repo my car . This morning Mr Theo Lombaard (credit control manager) phoned me and I explained the situation with the signed quote and he said he can't do anything and in addition also threatened to repo my car if I do not pay the arrears? I offered to pay R100.00 pm towards the arrears and he rejected, but accept on R 150.00 pm.