Ambiguous communication to client on premium

I added my newborn in June 2023 and on the 14th of June I received an email with welcome pack from Discovery. It stated the commencement and new premium. On my July payslip I saw that Discovery deducted +/-R9000 as a premium. Discovery what does FAIS and Medical schemes Acts say about clear communication that is not ambiguous. The nerve of someone from Discovery saying it’s my fault I should have known the letter was incorrect, do I work for Discovery?. Useless company that doesn’t take responsibility for its nonsense. I want a refund because I will pay the premium stated on the letter sent until they sent me an amended letter with the amended premium.