Tom loaned $$20,000$ to Paul, repayable one year later with $9\%$ interest. The loan was made on March $1^{st}.$ On March $1^{st}$ of the next year, Paul did not make repayment. The next day Tom visited Paul and said to him: $"$If you will repay me the principal of the loan today, I'll cancel the interest and close the entire matter." Paul assented to this proposal and, in compliance therewith, paid $$20,000$ to Tom on March $2^{nd}.$ A few days later Tom demanded $$1,800$ more from Paul, but Paul refused to pay. Tom then sued Paul to recover the $$1,800$ interest. Should Tom recover?