You need to make sure you are paying the current bill or the previous bill!
The current credit card bill date refers to the amount between the last month’s bill date and the current bill date. Most bank statements are 10 to 20 days after the last repayment date. Repay the credit card before the last repayment date. No interest will be deducted from the payment!
The interest charged to you is probably because your last period’s bill has not been paid off and the current period’s bill has already been generated. It may be that it has passed the last payment date of the previous period!
You can call the bank’s customer service number to confirm. At least under normal circumstances, no interest will be charged for repayment on the bill day. This is for sure!