Fedhealth holding onto money to which it has no claim

My parents were with Fedhealth for some thirty years. During the COVID lockdown I took my mother (my Dad had died) away with me to a farm to weather the lockdown. Unbeknown to me, Fedhealth had changed her premium and, despite efforts by my wife and I to find out what was actually due and keep paying it (with no replies) they terminated her cover. They are still holding R27 000 of her money paid in premiums. They refuse to pay it back unless we prove every payment made! Luckily I have her now on my Medical Aid, a far better scheme called Camaf, but I am furious with how they cling to her money having walked away from her just when she needed them most.