MTN have been busy billing me incorrectly

I took a contract phone with Nashua Mobile before everything was transferred to MTN. MTN did take over and things continued as normal, but in March things did changed. I was surprised by their billing and when I called I was told that I have subscribed for extra data and told the person who was assisting me to check clearly as I knew I didn't. They did apologised for the mistake done and promised to refund by reducing premium for the next coming month. I went and upgrade my phone and I signed another contract with another premium only for data. First premium was fine as per contract I've signed, but then the second premium was double the amount of my signed contract, when I call no one was there to assist as employees were on strike and when I visited local store I was told that the<br> is because my contract was from Nashua, new things to me as it wasn't stated in my contract. I went to another mtn store, I was as as told to call 808 which is their call centre and mind you no one was there at that time, until one day when I call to find the agent who told me that the reason why my premium was double is because of Nashua and when said the with he was talking about I didn't signed