Send the lawyer a certified letter requesting proof that this bill was paid and a copy of the canceled check. Give them a deadline to reply with the documents, if they ignore, consider getting assistance from your state bar associatio
Yes, call the state bar and have them call the attorney. They will get the proof you need, if it exists. If it doesn't exist, you will owe the bill ultimately. You can either pay it and file a small claims action against the attorney to get your money back or let the collections agency sue you and file a cross-complaint for indemnity against the attorney.
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