Debits whatever they please from my account

I've been insured with Miway for over 3 years now and I've never claimed, so we just recently purchased a new car and I decided to stay with Miway, my new premium more than doubled which was okay with me because of the car it is. However after agreeing to my new premium I was informed that a pro rata amount would be debited and was told the amount however when they debited almost double the amount I was told about leaving my bank account on a negative balance and I didn't get an apology until I demanded one, I was refunded the extra money. So now my first proper debit order which is not pro rata went off on Saturday and GUESS WHAT it's an incorrect amount, an amount I didn't agree to and that amount is not even in my policy schedule, so basically my insurance company which I've trusted with my bank information basically does as they please with my money, I feel like I'm insured with ************, this is such an inconvenience. I've decided to look for another insurance company, if Miway can't get simple changes right I'd hate to see what happens when you claim.