No Agreement!!!!!

I have been paying m Std Bank Credit card with DMC via direct deposit. I have made arrangments to pay R50 per month, today i receive a sms saying that I must pay R560 by the 28th!!!! I made no arrangements to pay R560 per month!!!! I called the call centre, but I was put on hold until I ran out of airtime!!!!! <br> <br> Is DMC going to reimburse me for my airtime???<br> <br> This company is ridiculous and I have heard from other people that they do not respond to emails and queries etc. DMC could just call me and ask me if I can increase my installments before sending a sms!!!<br> <br> I want feedback immediately from DMC!!!! They seem to be doing things that are out of the books!!!