MTN upgrading contracts at higher cost without consent

MTN migrated my contract with them at a higher charge without any consent. I have been complaining to them about it for the last month. Today they invoiced me the higher amount again and then suspended my account. I had to pay the additional amount just to try and get my number reactivated. But I'm still suspended. Now I'm going to travel and my clients won't be able to get hold of me. Terrible service