If they didn't look over the documents they gave you to sign at the time of adoption, that's on them - you're under no obligation to sign anything else now that you're already the owner of the animal. They have no legal foot to stand on - that doesn't mean they can't make life difficult if they want to, but if it went to court, their complaint would be thrown out because THEY neglected to give you the documents they wanted you to sign, and your signature is already on something else. I hope you have a copy of whatever you DID sign for your records!