Account in default after asking for invoice to make payment. This cannot be legal!!!!!!!

I have, on numerous occasions, requested for an invoice for an outstanding account to be sent so I can make payment. This has been ignored and I have been harrassed for the last while (whilst asking each time for invoices). Now the account is in default.

You send invoice, client pays. Not you send statement without details as to what I am being charged for and I pay!!! How is that so difficult to understand.

This had better not affect my credit rating!!! Have a competent person phone me to sort the matter out and I am still waiting for invoices!!!!!