Debt collector - calling for debt that is not mine

How to handle? Debt collector is trying to collect HVAC debt from me that is not mine - I sold the house in 2009 and they have my name on the account because we must have used this company at some point as well as the new owner's name. The work (a $200 service call) was done by the new owner in 2020. I called the HVAC company and they gave me some nonsense answer like if my name is on the account I must owe it. I can send to them the county record showing the sale of the house or what else do you suggest??? The HVAC firm sent me the invoice. It shows my name. I dont even live in the same state???