the Plaintiff, Henry Schindler, wrote the Defendant, Cooperative Refinery Association, and advised them that it was his opinion that the $20,000.00 oil payment would be paid in full by the payment of the October 1950 oil runs which were paid on November 15th, 1950; that the Cooperative Refinery Association has denied receiving such a letter; that such a letter was addressed to the Cooperative Refinery Association, stamped and mailed at Stockton, Kansas, with the scrivener's return address thereon, and the letter was never returned to him.
"12. That in August of 1949, Plaintiffs and those whom they represent, entered into a drilling contract with the Sterling Drilling Company, of Sterling, Kansas, for the purpose of drilling additional wells on said lease, for which drilling it was agreed that thecommenced within three years from date of the first over-payment, and therefore was not barred by the Statute of Limitations.
"4. That the over-payment to the defendant, Elsie Ross, was made under mistake of fact, and therefore was not a voluntary payment.
"5. That Plaintiff, Henry Schindler, had no reason to believe that upon payment of the $20,000.00 oil payment in full, and especially after writing his first letter in December of 1950, to the Cooperative Refinery Association, that said Cooperative Refinery Association would not stop making payments on said oil payment, and would not divert at least 75% of the 1/8th of the 7/8ths working interest which had been previously pledged to the said oil payment, to the Sterling Drilling Company, as per their contract with Sterling Drilling Company,