Cancelled reception fee

Did you make some payments to secure the venue that they are not refunding or did they have some other sort of fees?

If they have had to cover some costs like insurance or personnel, then certain costs should be paid by you. Also, it seems nicer that there is no contract since the vendors usually make a contract that is harsher. But it will help others answer your question if you mention what type of payments were made and what fees were waived

If you have agreed in writing, then if they take any legal action they can and will use that as an informal contract. If you didn't discuss an amount you can negotiate that.