@FranandZoeCall the drug manufacturer. You may be asked to provide the drug lot number, expiration date, and length of time that the drug was exposed to extreme temperatures.
I wouldn't take Lipitor that was expired unless the drug manufacturer said it was OK to. I take Lipitor/Atorvastatin and would be worried also if it had lost its potency.
Also there are many pharmacies that have a very low cost for atorvastatin. Last month I got mine for free from CVS.
Good luck!