Poor customer service/changing contract limits without agreement.

I signed a contract with MTN for R79. When I got the Sim, I received an sms saying the limit is set for R131,00 over the R79 which I called their 135 number and sent from pillar to post for one hour 10 minutes because I want to pay R79 as agreed but they say they're unable to set it because of their systems. My problem is that I can't afford a contract of more than R79 for 24 months. I wanted them to set it to exactly R79 which they are not able to do but I didn't agree with them on the limit of R131,00. They ended up giving me this .Ref *** saying they will do it. But am not happy with it because I have to be sent from pillar to post for more than an hour and still didn't get helped. May you please intervene maybe it might help.

Regards Noko Mashiane ***