Lancet Accounts Department is useless

I have had some blood tests whilst in hospital. I received a SMS from lancet requesting payment. I emailed them requesting the invoice as a SMS is not submittable to my medical aid. a full week went by with no response except a follow up SMS. I then contacted Lancet and requested the invoice. I gave them my email address and medical aid number. They indicated that they would submit the claim to the medical aid and would revert back if there is a problem. One week later and another SMS. Is there a problem understanding english here? I will not pay an SMS. Send thee invoice.......