Im being forced to stay where I dont want to stay

I made a call yesterday to discoivery Medical Aid. My plan is to upgrade my current medical plan to high plan. Im moving my daughter out of the medicxal aid. As my company pays for the full medical aid I decided let me upgrade. To my surprise I cant upgrade, why? Because discovery has decided not to allow me to upgrade. I have to wait till September to upgrade my plan. This doesn't sit well with me. Because discovery decided not to increase their premium they decided that its best for them to just force us to stay in a plan until they feel comfortable we can increase. I want to upgrade my plan effective the 1st of May 2022. Even if you have to make me sign an agreement that I wont downgrade for the next 18months I will. Im loosing out on my company benefits.