Fedhealth still to pay legitimate claim after almost a year of submissions

I have tried to handle my widowed mom's medical admin since a fall last year in August which required the services of a caregiver. This was approved ,but Fedhealth got the dates wrong after a whole backward forward game as I had to be authorised to act on her behalf. She broke her dominant arm and couldn't sign. We had to pay and claim back. The provider has submitted the claims numerous times starting in August last year. We had to sort out the authorisation dates because of Fedhealth's error. The provider kept having to fix things on her invoices which were apparently correct by December and then not correct anymore by January. Finally they paid one invoice in June and then another a while later after all were resubmitted yet again with codes changed according to Fedhealth's instructions. Now she has been told the claim is stale and has to submit proof of timeous submission and has to wade through 11 months of correspondence to prove this when all invoices were submitted together from the start. We have literally between us spent hours on the phone and using other communication to Fedhealth because of the ineptness of Fedhealth who kept just blaming the provider. My mom is on Fedhealth's top plan, Maxima plus, but service is abominable to say the least. I have 63 emails to wade through in the hope that they may finally do due diligence and pay what they promised before we hit the one year mark in two weeks. Note this is not our first problem with Fedhealth, but we thankfully eventually managed to come right with those ones.