The offer you get is NOT a lifetime deal, it is for x number of months. It then returns to the full retail price unless you play the “cancel” game to get a retention deal, which will be for another x number of months.
That is the standard price. If you keep an eye on your membership in My Account it will tell you exactly what the next payment is and when any discounts run out. Try cancelling and see if they offer you a better deal to stay, you may need to press the button a few times to see what happens.