Wowcher that doesnt seem to exist

I purchased a Wowcher a few months ago for a non surgical medical procedure supposedly in Harley Street. I emailed the official address on the voucher as advised to do so but had nothing back and so a couple of weeks ago I happened to be in the area around Oxford St so I decided to pop in and book the appointment in person. Anyway I was advised to go to the top floor which I did and found one tiny door all locked up and no sign of life. I then left my name and number with a lady downstairs and explained my predicament and she said she would pass it on to the lady concerned on the Tuesday following as she only worked on a Tuesday. Anyway following no response I emailed yet again to book in for the procedure as I did not want to lose £500 paid (despite having little confidence in her work given the empty room in the loft of a building and no contact from her) and still nothing. I wrote to Wowcher a few times and just get an automated response telling me to wait for my goods! Out of desperation I have claimed my Wowcher credit but have only received £250 which is half the money. Now this is theft surely as it is not my fault I did not get the service I paid for. Wowcher ignore my requests and now I only have a couple of weeks in which to spend the credit given and don't have faith in putting it in another so called service offered. Can anyone help or advise on what to do next? Thank you all in advance