Unauthorised premium increase

My husband pays our sons Key Care Plus medical aid monthly because our son is still unemployed and studying online. Suddenly this month, his premium increased with more than double the amount. My son received a sms message to update income with a link in the message. Because of all the ***** with messages received with *****ulent links, he did not open the link for security purposes. Which I in any case think is an unprofessional way to communicate with customers. After noticing the increase in the premium, we opened the link. According to them they did an independant investigation and decided to increase the premium. I would love to know based on what did they decide to initiate the increase. The monthly premium for both my unemployed children are deducted from my husbands account. This is unacceptable and need the premium reversed as soon as possible. So far Discovery did not disappoint but this 1 incident is enough to make ones blood boil. We already pay a lot of money for medical aids which we do not even use that often, then this happens