Have Foxtons offered you a solution to this?

Presumably this was a mistake on Foxtons part (rather than you providing them with incorrect account details), so they should talk to the bank where the money has ended up and get the money refunded to them, and then they can pay your money to you correctly.

Is it not legal for the person who received the money to hold onto it, so there should be no problem getting it returned, it's just a question of finding out where it has gone to.

But I think you'll need Foxtons assistance on this, because they will have to tell the bank it's been paid into the wrong account. Good luck.