No excuses. Pay up

Last week I received a letter of demand from a lab I went to in 2018. I was told discovery didn't settle the bill back then and now I have to pay. I was very alarmed because I have never missed any payments to discovery and I go to the doctor that they recommended. I then called their call centre and they referred my query to claims and the feedback I got was my claim is not gonna be paid because I went to do blood tests on the 3rd of July but I only activated my maternity benefits on the 18th of July. Now I did a few tests on the day and some were paid but there's one of R500 and some change that wasn't paid. The story of me activating my benefits late is nonsense and I refuse to accept it. I cannot pay thousands to your organization every single month and you can't pay a lousy R500 which is a drop in the ocean for you. Pay up and stop making excuses. Ref no is ***