I think it clearly states in the rules and regulations that once you have recieved a bid you cannot change anything except add details or photo's. I am a seller on ebay and this is what it said to me when I went to put a Buy it now price down. I didn't realize I had a bid on the item and I thought ah well no biggy.. It should have been done properly in the first place.. You won the auction so you should get the pram, It is not your fault they stuffed up

Def take up a dispute with ebay.. and they shouldn't be able to leave neg feedback either