You have few options
There are a few things you can try, but you should know that there’s nothing you can do to force them to remove the item from your credit report. It is legit, even if the circumstances are rather unfair.
This is a good example why closing accounts should NOT be done over the phone – because you have no paper trail. In the future, close accounts by letter and request written confirmation that the account is closed and the balance is zero.
There is no excuse, on their part, for them to not bill you for the accumulated interest, nor for failing to send you a statement in time.
I imagine that what you got charged for is called R.R.I.C. – Recurring Revolving Interest Charges. If you pay on the due date, it takes 3-4 days to process the payment. You get charged for the interest on this time period, which will appear in the next month’s statement.
What I would do is to sent a letter to the credit card company, protesting this reported late payment based on their representative failure telling you that the account is closed in good standing, and their failure to send you a statement. It might not do any good, but worth a try.
If this doesn’t help, try to dispute it with the credit bureaus. You have a slim chance of actually removing it, but if the dispute is rejected, you have a right to add a 100 word statement to your report, explaining your position. It won’t raise your score, but creditors will review it and it may help in future applications.
Please do come back and tell us if and how the problem was resolved.
Good luck