If the other party has approved it, either verbally or by SMS, you can also take similar measures to get payment. You can further collect evidence and then defend your rights through litigation.
The statement can be used as evidence for prosecution. If the company authorizes an individual, it can be stamped with the company seal. As for the signature or seal of the legal representative, it does not matter. If the company is not stamped and signed by the legal representative, it should also be considered effective, that is, it will be stamped with the private seal of the legal representative.