Refund still waiting

British Airways cancelled my flight for 3 people, gave me an evoucher, tried to use it how many times but no more domestic flights, we phoned how many times for the refund, and today again, no email or calls to get refund as they no, the customer service that my bank details has changed. After there 28 days still nothing and then after this morning they sending it again to refund department. How long must we wait 28 days is months already. Every time phone this time back or sorry we don't refunds, if you phone in again then o surr we will send it to refund department. ****py service