Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
Lets try a three step process here, and this should fix the issue.
First, tap and hold the pandora app on your iphone till it begins to wiggle, then drag it to the trash.
Next, press and hold the sleep / wake and the home button on the iphone for 15 seconds until it turns off, and then back on.
Finally, go to the app store and download and reinstall the pandora app.. Once installed, open it and sign into your account.. Hopefully, all should be well at this point.
If you get stuck at any point please send a detailed reply letting me know what happened so I can assist you further. Otherwise, if all works out please remember to return here and click and submit a 5 star rating to show I was able to assist you.
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied. If you do not submit a rating, I am in no way credited for my time. I always answer follow up questions.Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.