It seems wrong to inform ABC of the loan and repayment by SMS.

Borrowing from a bank requires not only repayment of principal, but also repayment of interest. What you do in the bank is to repay the loan in equal installments every month, that is, the principal plus interest you repay every month is the same amount. Bank deductions include principal and interest, with more than 500 yuan per month as principal and the rest as interest. As you repay the loan every month, the principal balance is decreasing, and the interest to be repaid every month will also decrease. In the case of equal repayment, the principal to be repaid will increase every month, so the principal deducted by the bank will increase every month.