British Airways (BA) Refuses to Refund my Money Even Though Flights Are Grounded

I had booked flights for July 2021 through BA but when we moved from level 3 back to 4 in June 2021 the flights were cancelled. At the time I received an email prompting me to either get a refund or a voucher to travel at a later date. Since I knew I would take the trip once we moved back to level 3, I opted for a voucher. We are now on level 3 and I want to plan my trip for August 2021 but BA has grounded all their flights until September - this is information I was not made privy to. Now, I want a refund to the value of my voucher because I want to book with another airline that is operational in August 2021 but they are refusing to refund my voucher because they are not refundable per their ordinary business practices/procedures but what is currently happening is out of the ordinary so, my question is why must I as the customer be limited in when I can plan my trip because they have failed to plan for the extra ordinary? I WANT MY MONEY BACK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!