BA Voucher vs Refund - Unacceptable

IanGullers

Hi, I bought flights with BA to Thailand flying at the beginning of April 2020.  I paid for the flights on my debit card (I know I should have used a credit card) last October.  I made additional payment to change our outbound flight date and then further sums of money to secure seats next to my partner for outbound and return. The return flights were business class, so shouldn't have to pay to secure seats, but that is another issue.

When the FCO issued a ban on all international travel and flights were cancelled, I selected the only option made available by BA on the Manage My Booking page which was a voucher for future travel.  There was no other option.  The voucher did not arrive so I contacted BA and spoke to Customer services.  I explained that I hadn't received the voucher and that I would like a refund instead - I didnt see that we would be able to take advantage of the voucher.  The customer services representative pointed me to the make a claim section of the BA website and said that my ticket would be eligible for a full refund.  I made the claim and BA Customer Relations responded to say that because I had selected the voucher I could not have a refund.  I have responded back to say this is unacceptable given the only option made available to me was a voucher - they are sticking to their guns and refusing me a refund.  Furthermore the voucher is for the cost of the original booking and does include any money paid for seat reservations or altering the outbound date - a total of over £1,300 extra.  Is there anything I can do to claim/ force BA into granting a refund? Can I claim on my travel insurance instead?
Thanks