They approved preauthorization for surgery but now they refusing to pay

I have a profound hearing loss bilateral. I was using hearing aids which were not helping much, when we got hit by the pandemic my life changed forever. Because now everyone wears a mask I am unable to communicate as I mostly lip read. In the beginning of June I went to a n ENT which suggested that I a cochlear implant, we contacted my medical aid ( bankmed/discovery) for preauthorization and they approved everything. On the 23rd of June I went for surgery which went well and was told to come after 4 weeks for the activation on the sound device. I'm sitting here at home 6 weeks later with no device because my medical aid is now refusing to pay for the sound device. My hearing loss became worse after the surgery, which has caused me to stop working, we were all under an impression that the whole process will take few weeks. I really don't hane money for the sound device and bankmed has failed me