Trouble during payment process: Mortgage

HI i have santander overdraft HELOC. I paid it off it has a $8500.00 line of credit. The problem is after I paid it off a $20.00 dollar interest was assessed. I didnt pay it as I thought the account is fully paid up. This cuased additional $28.00 interest to be assessed to my account and it hit my credit score hard with a 60 day late. Im asking Santander to remove it from my credit bureua as I already paid it off and I was a good paying customer this is merely an oversight with a minimal amount of interest due.