In order to reschedule your cancelled exam (due to weather), you will need to use the Schedule link on Prometric (not the Reschedule link) in case you can't get through to Prometric. It will say no money is to be charged.
Do not use the Reschedule link because it will tell you that you can't reschedule (on or after the original test date) or it will try to charge you (on the day you were told that the test was cancelled).