Dual insurance refund

I joined Discovery Insure in April this year, when I joined Discovery Insure assured me that they have a department that deals with cancellation of existing insurance policies, and they promised that they will call my existing insurer and do the cancelltion on my behalf. However this was not done because for two months my I was debited by both Discovery and my previous insurer. I then went on to call them and requested them to do the cancellation, they promised that they will do the cancellation and also promised to refund me for the period when I was dually insured. They explained to me that, by law, an insured cannot be insured by more than one insurance company, and therefore both Discovery and the previous insurer are each oblidged to refund me 50% of the premiums debited during the time i was dually insured. I ended up doing the cancellation myself with my previous insurer, I also sent them all the documents they requested for my refund and I was refunded within 2 business days. On the same day i sent all the required documents to Discovery for the refund, this was 26/05/2021, they responded to say the issue will be resolved within 5-7 working days, I sent a follow up email on 08/06/2021, till today this has not been resolved.