Bad Service/ Incorrect Premiums

I phoned in to cancel my policy, firstly the premiums as confirmed with the consultant were incorrectly debited for June, I was refunded the difference after fighting with them. I then realized that they have debited me with the incorrect premiums end of June. I cancelled my cover with them ASAP but they debited my account on the 27th of June and again on the 7th of July 2015 and it was unpaid as I did not have sufficient funds. I was charged by the bank for unpaid and advised Alex on this and he told me to get the bank statement and send him as proof so that he can refund me the charges. I went to the bank and requested the bank statement but it does not show the charges separately for each transaction. I then phone the bank and asked them how much are the charges for unpaid and I told him. He said he cannot refund me because there is no proof that they charged me for unpaid. But it does show on the statement the unpaid debits. He is ignorance and does not want to co-operate and he thinks he knows everything. I have never received such bad service and I wish I have never taken the car insurance with them. Finally after so many calls, the policy has been cancelled.