No clue how to handle accounts

Ampath only communicate via SMS and make it their clients responsibility to sort out accounts. No invoices are sent and the sms is a demand for payment even though it may be the first notice of an outstanding amount. The statement link cannot be accessed and everytime I have made a payment I then need to go through a refund process for the same amount. Ampath have no clue what is happening with their accounts and I will not willingly use them in future.