I have also been being double charged for Pandora by Google. It has been going on for about 7 months now. I have reached out through email (because you cannot contact Pandora by phone) and they were unable to help me. I tried calling the Google number on my bill but that number really does not let you get to a person either. I have disputed the charges with my credit card company.
It seems like this is something that is happening to a lot of people. There is an obvious problem with double charging for Pandora. It does not seem as though they are in any hurry to rectify the situation