Opodo complaint: Tickets not refunded

I entered into an agreement with your company on 24012020 booking reference number 4956730831 which were return flights to Nairobi and Mombasa departing from London Heathrow on the 4th of August costing a total of £3229.47 which I fully paid to you.
On the 13 of July, I was notified by you that the airline had cancelled my flight and that you were looking at refunding my tickets in the form of vouchers. You last emailed me on the 3rd Of December 2020 telling me you were still awaiting a refund from the airline, which was taking more than 3 months, clearly by then it was more than 3 months since my flight had been cancelled by them
In March I requested a chargeback from my credit card to which you recently appealed against it which means I still haven’t got my payment refunded for the cancelled flights for my family and I.
Your term(s) constitute an essential part of the contract which to date this has not been fulfilled. I am requesting your company to honour the contract within 14 days from the date of this letter. Otherwise, I will have no option but to cancel the contract without incurring penalties.