I have had my card used fraudulently recently.
I rang because like you I suddenly found I had a LOT less money that I should have had.
The bank passed the details on to their fraud department. They would not give me my money back before they had investigated, but they did increase my overdraft by the value of the dodgy transaction so that I had enough money to live on.
After a couple of weeks I was sent a form by the fraud dept where I had to circle the payments which were frauds and then sign to confirm this. I got the money back immediately. I don't know what else will happen. Like you, I wondered if it was an inside job (ie someone at the bank) for reasons I will not go into here.
Obviously my debit card had to be cancelled and with the new debit card came a "terms and conditions" booklet which stated that if it is proved that a fraud has taken place you are only liable for up to £50. But I have not had to pay £50.
So, in a nutshell you need to get back to the bank, say that your card has been used fraudulently, it has been reported to the police, you want them to investigate and in the meantime you need some money. Don't take "oh you have to talk to Play.com" for an answer. Play.com might have asked the bank for your money, it's your bank who gave it to them without your consent and presumably without the proper security code. It is absolutely the bank's problem.
If you get no joy from the person you speak to, ask to speak to a supervisor.
What with one thing or another recently, I have been on to my bank a lot (I can do telephone banking). I would say that out of the last five things I have asked them to sort out for me, in the case of four of them I was given the totally wrong information the first time I asked. I mean basic stuff, like being told I couldn't do a foreign money transfer over the phone, I'd have to write a letter. Phoned back to ask what exactly to put in the letter - told: oh you can do it over the phone. Two days later tried to transfer some money over the phone to an account with the same bank, in the same country, and the bloke was adamant that I couldn't do it over the phone. Etc.
So please try and try again. You probably just got someone who doesn't know their arse from their elbow.
Good luck.