We'll cover immunisation only up to 9 months

My son recently turned 18 months which meant it was time to have his immunisation in accordance with Department of Health's Programme on Immunisation. I usually have this done at Dischem as its convenient. My plan always covered for immunisation. The problem occurred on Wed Jan 20 where the claim couldn't be processed on Dischem's system it advised that the claim had to be submitted through Discovery as they are the new administrators. We couldn't further proceed as there was a technical error. I contacted Bankmed & they advised that the claim went through but was reversed & that they were aware of the technical issue. The following day I returned to Dischem & advised the nurse to contact Bankmed to process the claim they in turn referred us to Discovery, we spent an entire hour and a half being pushed from pillar to post trying to have this resolved, the claim then stated that the Vaccine was not covered on my plan this was quite surprising as the previous claim 9 months vaccine which had the exact same vaccine was processed successfully so the scheme claims they cover 100% if its according to the Department of Health guidelines? Why was my claim rejected please explain?