I've been told the following by a UK contact who regularly obtains money for punters when it is being witheld unfairly from them by UK licensed gambling companies:

"If you're based in the UK and have not been paid it is probably worth contacting https://www.actionfraud.police.uk/ which is a specialist police service for cybercrime including fraud.

It is also worth contacting the UK Gambling Commission, because Anybet.eu are not regulated by them and it is therefore illegal to trade with UK based customers. The UKGC will not help with individual cases, but it is their duty to investigate companies who offer gambling services illegally in the UK. This may help everyone in the medium term.

The big difference here to my usual work is that Anybet.eu is not UK regulated or I would recommend other options, but these two would seem sensible to start with and if they fail there is the option of group legal action."