Held hostage to pay for a service i dont need.

I have been a premium subscriber for 6yrs now n it wasnt a pleasant 6yrs. The amount for their packages is always fluctuating, i don’t even know what my premium is anymore as im currently owing R1100. Yet i never missed a payment. Now i cant afford this premium anyomre and i tried to downgrade n guess what... They have made up some ridiculous rules like “you can upgrade your package any day but you can only downgrade on your date of payment.” My payment date is the 15th, today is the 17th, n they say I cannot downgrade i have to pay the full amount. Why cant I downgrade and pay pro-lata for the 2days that passed? Why must i pay for something i dont want? We didn’t sign any contract about this. I don’t owe them payment for a service i dont wanna received! They are indirectly forcing me to give them a one month notice before downgrading as if this is some credit agreement and yet their payments are upfront payments!