Over charged premium

In December I was charged 757 for a premium of 499. I phoned them and asked why am I being charged that amount and the agent told me the is escalated to the relevant department and they will phone me back. I waited no call or anything from that so called relevant department. Now today the 14th January I being charged 628. I called again to find out why, no one could give me the reason as to why. Multi choice they are the worst and when you call the call center you being transferred from one department to the other with no answer.