BA delaying refund for flight they cancelled

I recently traveled to England with BA. Once there BA cancelled my flight - I app**** for a refund on 31 December 2020 and am now told I must wait 4 to 5 weeks to received a refund. I have sent many mails to BA but I regret to say that they are using Covid 19 as an excuse for delaying the refund. Of course I had to buy a much more expensive 1 way ticket back to SA and had to pay for that immediately. So not only did it cost me nearly twice as much to return, they now add insult to injury by not refunding my money timeously. All flight details are computerised - their no need for them to check anything other than ticket was not use - which it could not be as they cancelled.BA has no CUSTOMER SERVICE and are very difficult to talk to - all leave a message and we will contact you. PATHETIC