Because the customer writes the receipt in his own name without official seal, and his successful impersonation is not due to your company's fault, and it does not belong to the "agency by estoppel" in civil law, your company does not need to bear the responsibility for its behavior.
This is employee fraud, not yours.
And: the above handling opinion is that this case is an agency by estoppel, but the agency by estoppel requires that the principal is at fault and the other party is not at fault, which is not applicable to this case.