poor service

i have a discovery medical aid Mmed option my son was in hospital in January for 4 days. in may month i received a final demand from pathcare that they their claim was rejected by discovery i need to pay them immediately . i sent the claim to discovery and the response i got from them is that my claim is late, so i asked them why did they reject the pathcare's claim, discovery said never got the claim they suggested that i should get proof the path care did send through their claim. i called path care to get the proof and i sent it to discovery immediately and i got the same response that it is too late claim. i have done what they asked to do but they didn't even provide me with the reason why they rejected the claim from the first place.