Charged for upgrade without benefit

On 20 March i visited the MTN Morningside branch to change my contract to incease the usage limits. I signed a contract and was given a copy as I requested one but it was not offered one. As I was not given the benefit of the proportionate upgrade i went in on 22 March to complain. The matter was not resolved but escalated. Still nothing happenedwhen I complained on 26 and 27 March. When I got my account I have charged for March as if the change took place on 1 March - not a proportionate charge as promised. I have called on 9, 12 and 25 April to resolve without success. I have a reference, and the full names of the consultant and supervisors I have spoken to on all occassions. I have reffered the mattter to supervisors as the promise, haha, is to resolve in 48 hours which after waiting so long is unacceptable! Tis organisation are ****** and are not at all interested inresolving issues which cannot be escalted even if you ask! They are "*****ing" money without fear of consequences, clearly taking a leaf out of the Government's book! How do you resolve issues with them. My call today was 35 minutes and no headway!? What does one do?