If a cellular service is disconnected becasue of lack of payment, can
the wireless company providing the service legally charge 2-times the
past due ammount in order to reinstate the service?

If a cellular service is disconnected becasue of lack of payment, can
the wireless company providing the service legally continue to charge
you the regular fee for the service?

Likely they can do either or both in most USA locations. You should
avoid one and two year contracts with cell phone providers unless you
are reasonably sure you can make all the payments. Worse they can
stick you for a $100 replacement cost for a phone that quits working
before your contract ends.   Neil