GEMS WRONG ALLOCATIONS

Good day

I have since I am on pension paid more each month, I was not behind in payments. Now suddenly I am R3301 behind. I phoned GEMS and they informed me that there was a wrong allocation made on the 28 April 2023 and they only saw it now. So now I must pay that arrears, the fault of someone at GEMS how made a wrong allocation in April 2023. So my question now is who is suppose to take responsibility for this. I must now pay this arrears back our my medical aid will be suspended.