Nightmare with our venue

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Hi

Can anyone help. We went to a venue and were told we could have a main course hot fork buffet for £19.95 with free room hire if we had 100 people we were advised that there was going to be a price increase of no more than 10% which they are now denying. We paid our deposit in March and booked the venue for 13th June 2009 i got a phone call yesterday saying that this option was no longer available and we would have to pay £29pp for a 3 course hot fork buffet i have tried to negioate and asked for welcome drinks or toast drinks instead of the start and dessert but they have said no and that we have to pay full price for children as well. There is no contract but can they do this after we have paid our deposit.

Del