Sizwe doesn't pay hospital bills even when authorised

We treated a child in August 2017 and have been trying to claw payment out of medical aid since then. They have paid most of the account except for one date in the middle of the treatment period. The treatment was a hospital authorized treatment When I email them, they do not respond at all other than to get a email to say it has been received. When I call, they say they have sent the date for processing but a month later the account is still not paid. When I call again and press all the buttons to get to the relevant section, I then get cut off and no one answers. I am frustrated at their lack of service.