MTN I have a 36 mo...

MTN I have a 36 months contract with them and I got a call last year of a lady telling me that they gonna top up my account and I declined the offer then Jan they debited 713 when I called I was told they migrated me to a top up account and I clearly stated NO Then when I call and try to get the matter resolved no help is rendered they keep on transferring me to another department which they will say they can’t assist me so how can I get them to take me back to my 430 that we agreed on cause I never agreed to the 713