Poor service

Last year I wrote to Fedhealth on the 03 October 2022 requesting that pay the October premium in two,half mid-October and half at the end of October with November premium and they did not respond to my email,and I've paid as per my request but they went ahead and suspend my membership without communicating with me. I tried to buy medication on two occasions and I was told my account was suspended,then I wrote to them and they responded by saying my account was in arrears and I forwarded the proof of payment several times,even at the period I app**** for an option change and I was told the same thing that my account was in arrears and I had to forward the same proof of payment. Then on the 13 December 2022 I was sent a correspondence that my membership was lifted and I tried buying medication at a pharmacy and I was told my membership was still suspended. Early this year I called them and was told the error was from their side as the funds were mistakenly allocated to my medivault account and they apologized and fixed the issue. So my issue now is that they are refusing to change my option because the window period for the change is closed. Who's fault is it???