Arrear contribution letter for contribution already paid.

In February I submitted my notice to cancel my medical aid at end of April, i.e I gave over a month notice. I was changing employers/departments. I started at my new employer beginning of April. On the 15th April, the day I get paid, there was an amount of R5 166, 00 deducted for GEMS. Which is fine since I was still covered for April until 31st. I was caught by surprise when I got an arrear contribution letter from GEMS informing me of my outstanding payment for April. I have been calling the whole of May got sent from pillar to post without ever getting much assistance. At 1st I was told that this contribution might be held by my employer and never made it to GEMS, the consultant i spoke to said she's requesting a reconciliation from the credit controller and we'll take it from there..that never happened. I kept following up and eventually got told that there's no arrear showing on the system and they further send a request to the credit controller to contact me. On the 25 May 2021 the credit controller called me to inform me that there is no arrears and my April contribution was received. I requested he sent me an email stating that. He never did. To my surprise I got another letter of arrear contribution. I called again, sent proof of my salary advice previously but nothing has happened. I sent again today, hopefully they'll attend to it. Its frustrating and disappointing since I never had issues with GEMS before.