Ampath's disgusting service

I did some blood tests in July 2019 with Ampath Laboratory and they only submitted the claim in December 2019. My medical aid rejected the claim as they need proof of submission for July. Ampath is unable to provide my medical aid with the proof of submission as they claim that it was submitted by the hospital electronically and they do not have proof. Now Ampath tells me that i'm liable for the bill. How am i liable for their mistake? I'm paying the medical aid so i told them that they must not make their problem of incompetency mine. I do not work in their accounts department and i'm not paying a cent