Section 9 of the company's Ts & Cs seeks to prevent you from taking legal action against them to obtain a refund under the current circumstances:
https://www.cottages.com/assets/booking-conditions.pdf?v=7f070d7a7bcf8101f7c1cbe774bbf586
It would be up to a court to decide whether or not that section is actually valid.
All that you can do in your situation is all that anyone can do (not involving a couple of big guys with baseball bats) when someone else owes them money and they won't pay up. That's to threaten legal action and, if you still don't get your money back, to take the company to court via the small claims track.
Send a letter to Vacation Rentals (UK) Ltd at Spring Mill, Stoney Bank Road, Earby, Lancashire, BB94 0AA. Your letter should be sent by Royal Mail's 'Signed For' service (or if, due to the current situation, you can't actually get a signature, by any other tracked service which would enable you to prove to a court that your letter was sent and arrived). Your letter needs to clearly show:
(a) your name and address ;
(b) the company's name and address ;
(c) the date it was sent ;
(d) that it is demand for payment ;
(e) the amount demanded ;
(f) the reason for the demand ; and
(g) that, if payment in full is not received within a specified period (I suggest 28 days under the current circumstances), you will seek a County Court Judgment against the company.
If you don't receive a refund within the specified time period, commence legal proceedings using HM Court & Tribunals' online system:
https://www.moneyclaim.gov.uk/web/mcol/welcome