They do not give feedback

I called the call centre to amend my policy, which was done, however at the end of the month, they debited more than what was discussed. I called to find out why and no one can help me, they keep saying they will investigate and get back to me. I have requested a call back numerous times, but nobody gets back to me. They have now debited me again for the new month, but still no feedback about my query. If their service is like this regarding a simple query, I would hate to think about how they deal with claims, and to think I wanted to add another car to my policy! Now I would rather change my insurance company.