Request late charge removal for Xfinity error

I asked Xfinity to correct my mailing address to add my PO Box # because no bills were arriving by mail. They did that and ONE invoice arrived. This week I received an email late notice (but no actual bill). The account erroneously transposed two of the box numbers: no wonder I did not receive the bill. I am asking for reimbursement for two late charges to my account as a result of their error. The chat bot did not work.