I purchased a product from China and put it up for sale the was contacted by a company that says they own the patent. After looking up patent it says expired fee related. Patent number 7703235. It also says anticipated expiration of 2026-10-04. Did I infringe on this?
I'm assuming you are in the US as the cited patent is a US Patent. In any case, the USPTO Patent Center lists the patent's status as: "Patent Expired Due to NonPayment of Maintenance Fees Under 37 CFR 1.362 - 05/30/2022". I am not a lawyer, but this suggests to me that the patent is currently unenforceable. It may be that the patent owners can pay the fees and penalties and resurrect the patent, but I'm not at all sure that would be retroactively enforceable back to 5/30/2022.
There is always the question of whether the product you sold is actually covered by the claims of the cited patent. I wouldn't just assume the patent owner has confirmed that. Also, the same inventor has other patents that might be relevant. Did they cite the specific patent you specified or could they be enforcing another that is still in force?
Since I'm not a lawyer, this isn't legal advice. You might want to contact a patent attorney to confirm your status before you tell them to bug off.