overcharging

I have a MTN contract for 4 years, which is a top up. I receive data and airtime. Last month MTN took back my airtime and when I queried it they said I used it as data. This is not the case because in the past 4 years if my data was finished I purchased data. I loaded R160 airtime and the same thing happened. My contract was due for upgrade so I wanted to port to Vodacom. I could not do this because MTN was striking so I took a new contract with Vodacom. I get my MTN bill and now I am being charged R180 extra for calls. How can I be charged for calls on a top up contract. The consultants @ Simmons Street branch are ***** . They said that I am going to be charged only R180 but my bill is for R621. No one is prepared to assist me.<br>