GEMS MEDICAL AID

My son has been a dependent on my medical aid since 2009. He completed his studies and I sent in the dependency form in march. We went into lockdown thereafter. I did not receive any correspondence from the scheme to say that he has been removed. They say that they did not receive my letter. I dont have a proof because i sent it from my workplace. Their correspondence went to an email address that I dont use. I only realised that he was removed when ineeceived the new membership cards in the mail which excluded him as a member. I made a number of calls and sent in a letter explaining that I sent the form but they are not sympathetic. I even told them that I will pay the premiums for the past 4 months. There are no claims to be paid out by the scheme because he has not been to the doctor in the past 4 months. They are just adamant that because they did not receive the form that they cannot reinstate him. I explained to them that it was during the lockdown and there was no communication but to no avail. They now added him as a new member with a waiting period of 3 months and 12 months for preexisting conditions. I went on to explain that I had sent in all previous applications for dependency and they acknowledged that. I told the consultant that these are abnormal times and that they should be considerate but they are not willing to budge. I was told that they sent me a sms requesting the document but there was no such message sent to my phone. What is my next option?