How to find a Solution

We have encountered a problem in a case related to the column we posted the other day. 
This time, we are working as an agent of the seller and are proceeding with the contract procedure. The real estate is a refurbished property in Kita Ward, originally used for a guest house. As part of the asset consolidation, seller stopped the operation of the guest house, and when it was for sale, an individual customer in Tokyo applied for the purchase. 
We are an agent of the seller, and a customer in Tokyo was found by another real estate agent and applied after the property inspection. The buyer is an individual, and the seller is a general corporation in Japan. First of all, if there are two real estate agents, the seller's real estate agent will do the research of the real estate, the preparation of the explanation of important matters, and the preparation of the contract. In this case, it's us.

Since the real estate agent of the buyer guided the property on Sunday, applied for it on Monday, and had price negotiations, the seller presented a counter offer on Monday, and on Tuesday morning, the buyer confirmed the consent and confirmed to the seller. Then, the price of the mutual agreement was decided. The buyer's desired contract date is Thursday. Generally, the contract is concluded within 1 week to 10 days after applying. This is because the real estate survey needs to be done, so a contract two days after the agreement is a very short term.
This time, the contract will be carried around, and both parties will carry around the contract and get a signature stamp. Therefore, in this case, the buyer will first sign the contract on Thursday, and the seller will sign the contract later. It's a very short schedule. Also, real estate agents often have a off on Wednesdays, and the buyer's agent is also closed.
However, even if it is Wednesday, we need to complete and book the contract on the morning of the next day, so the contract will be prepared on Tuesday and the contents of the contract will be confirmed on the Wednesday.
During the day, we conducted field surveys of real estate, surveys related to government offices, and surveys that can be acquired on the Internet. We had to prepare the contract documents by the next morning.

The contents of the documents will be the contracts, document of explanation of important matters, equipment table preparation and status report, and boundary explanation documents. It will be completed in about 3 to 4 hours. We had confirmed in advance with the seller's corporate representative and secretary, but this corporation has two representative directors appointed, and we were hearing that the name of 100% investor will be used in the real estate sale contract.
After confirming the contract with the buyer, we bound the documents and delivered the documents to the agent office on Thursday morning and waited for the contract. During that time, we coordinated the necessary documents and interviews with the seller, and confirmed the necessary documents. And yesterday, Thursday, we asked the buyer to sign the contract safely, and received the 10% of sale value as deposit. The buyer's procedure is completed.
Then, we were contacted by the secretary today, and it became clear that the representative's seal stamp certificate was different from that of the representative stated in the contract. Yes, the seal was registered under the name of the other representative director. We can't prepare the seller's seal stamp certificate that is already written on the document signed by the buyer.