Hotels.com effectively acts as a travel agent, not as a hotel operator. Accordingly, your contract (if one ever existed) was ultimately with the hotel, not with Hotels.com.
As Hotels.com is an American company, any legal action against them would need to be carried out via the US courts (or, more specifically, in Texas). The registered office of the company is 10440 North Central Expressway, Suite 400, Dallas, Texas 75231.
If you phone Weston-super-Mare Tourist Information Office, they should be able to find you suitable accommodation:
01934 417117 (0900-1800)
Alternatively, The Richmond Hotel is generally well-reviewed in TripAdvisor
http://www.tripadviso...Somerset_England.html
and is available for 3 nights (Fri/Sat/Sun) for 2 people through Laterooms.com for £195
http://www.laterooms.com/
or the Walton Park Hotel, just down the road in Clevedon, is also worth considering for £173 from the Best Western website:
http://www.tripadviso...Somerset_England.html
http://www.bestwestern.co.uk/
Chris