You seem to have contravened prohibition 6.2 (j) of the company's T&Cs:
https://www.888ladies.com/terms-and-conditions/#YourPromises
Unless you could show that such a prohibition was 'unreasonable' in a court of law (which, as it seems perfectly sensible to me, I very much doubt that you could do), you've got no chance of getting the firm to pay out.
Prior to 1st September 2007 all gambling debts were unenforceable under English law. (i.e. you could win a million pounds at the bookies, or on the pools, but the bookmaker or pools company could say 'Tough luck, mate. We're not paying out" and there was absolutely nothing that you could do about it). Since that date, gambling debts are now covered by the same contract law as other debts but the courts won't rush to enforce them, especially where there seems to be a breach of the relevant contract by the person placing the bet (as in your case).