The key is the evidence:
First, you can find a witness to record the conversation with the seller, or make a telephone recording. The recording should indicate the time, place, on-site witness, the amount of house payment and the delivery method, so as to prove the fact of buying a house.
Second, the house payment is not a small amount. You can go to the bank to print the payment voucher, which will show your card number and the card number of the mad cow monster to prove the fact that you paid, thus proving the fact that the house purchase contract has been fulfilled. You can also find witnesses to confirm this.
Third, there is another way. You can find a trusted middleman to mediate, and the recording of the mediation process with all three parties present can be used as evidence for buying a house.
To sum up, on the basis of the above evidence, you can sue the other party and ask for transfer procedures. During the trial of a case, both parties may mediate under the auspices of the court. If they can't transfer the ownership, they can ask the other party for compensation, as long as both parties agree.
I suggest that everyone must go through the transfer formalities according to law after buying a house, so as not to cause any trouble.
I wish you get rid of your troubles as soon as possible!