MRP Sport Online refuses to refund me for goods they did not supply

I bought goods online. They took my money eventhough they did not have all the goods in stock - misrepresentation! This was on 20 November. They claim to have sent me a voucher for the difference - a lie. To date I've not received the voucher in my inbox. When I said I want the money back they said give us your bank details, which I have done. They then said 7 - 14 working days. Now, on day 14 they say 14 - 21 working days. This is theft. I am now going to the police station to open a case of theft