Booking.com not paying me

I haven't been paid an invoice which was due on 18th April, I received a message saying I should check with my bank and it was paid on 3rd April (2 weeks before it was due), and at a different amount, was given a 'SWIFT code which was entirely the wrong format for  SWIFT code and told to check with my bank. Upon a request for the name and account number to which it was sent, I have been ignored and further messages have been ignored. I'm still owed the money and no communication is now forthcoming. Have booking.com run out of funds? Do I have to start legal action? Why don't they respond to me. This, in comparison to Airbnb who sent me an ex-gratia payment of £626 to support me, Booking.com are actually withholding money, The difference between the two companies could not be more stark.