Re: Refused to sign invoice
You didn't mention the amount of the bill. I hope you cashed the check after you left!. There's no way this can come back to bite you. Don't worry about it. Where did you pick up this customer?
Work up an estimate now to replace the line and write the history of your original call and that you highly recommend replacing this defective pipe. Have it notorized and send it to them certified mail with return receipt. When it leaks again remind them of the price to replace it and you will require the entire amount up front (make it twice of what you would normally charge - just for the grief they have already caused).
If they insist the leak is on your pipe tell them to call someone else but you or your representative must be there when they uncover the pipe.
Put their name and number in your caller i.d. just so you will be prepared. Don't answer their call. Call them back.
"Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain