Shocking Accounts Department Service

We have dealt with TNT for international shipping for years and lately the customer service from their accounts department is shocking! We receive demanding emails and phone calls regarding unpaid accounts however we battle to get invoices! E-mails are ignored and phones are not answered. How can we pay our invoices on time if they are not sent to us after we beg for them? We used to receive all our invoices via email but lately it takes sometimes over a week to get anything after numerous phone calls and emails!! The frustration levels of my admin department staff are through the roof! This delays our costing process on our shipments which in turn delays our invoicing to our clients. Your online accounts portal is useless and invoices are not loaded. I can only find a few invoices and SARS documents from over 2 years ago!!! None of the new invoices are available to download.