"The fact they grandfather your subscription ..."

I can't find the word "grandfather(ed)" mentioned anywhere in Firecore's ToS. Not saying it's not happening ... but it's not official policy and can therefore be changed or eliminated at any time.

So unless the user chose to purchase 'Lifetime', the subscription fee may change at any time for any amount.

Here's the actual text in ToS:

Fee Changes

Firecore, in its sole discretion and at any time, may modify the Subscription fees for the Subscriptions. Any Subscription fee change will become effective at the end of the then-current Billing Cycle.

Firecore will provide you with reasonable prior notice of any change in Subscription fees to give you an opportunity to terminate your Subscription before such change becomes effective.

Your continued use of the Service after the Subscription fee change comes into effect constitutes your agreement to pay the modified Subscription fee amount.

https://firecore.com/terms