True. I know how you feel, and have TBH, given up on many similar situations.
BUT a recorded delivery letter saying "I understand that you have rejected my claim and we have reached deadlock on this situation. Unless I hear from you with a positive proposal within 7 days I will be taking the matter to the Small Claims Court for resolution of my claim, compensation for my time taken and Court fees." might produce a result. If they call your bluff, then you can give up at that point, or go online and start the process.
https://www.citizensadvice.org.uk/l...laims/deciding-whether-to-make-a-small-claim/
https://www.gov.uk/make-court-claim-for-money