Sell it (here, bike radar, gumtree, fleabay) and buy the bike you want
Remember the fleabay seller would have paid at least £78 in fees (assuming these are still *only* 10%) , so cleared £700 if lucky. I'd say that sounds like someone paid rather a lot for a 2010 bike but that's fleabay for you! You've not done many miles in the last 3 years or did it have a former owner? Assume you've tried all the usual tweaks to make it fit - stem, bars, cranks?
Why did you buy a carbon bike in the first place if so concerned about the material?! It's no weaker than any other in a big crash