@MrAcidic It sounds like your subscription is getting transferred due to your Google Play account being signed into multiple Android devices.
Transferring of subscriptions occurs when one or two people are using the same Google Play account on their Android devices, but different Pandora accounts. This can happen if you share your Google Play account with anyone, or use the same Google Play account to purchase apps on two Android devices. A subscription purchased with a particular Google Play account can only be applied to one Pandora account at a time.
To keep this from happening again, I would recommend that you let anyone who might use your Google Play account know that it would be best to upgrade to their own Pandora subscription from a web browser using a credit card, or to use a different Google Play account.
If there is no one else who could be using your Google Play account then you may be triggering this transfer by accidentally using two different Pandora accounts. Try signing out of Pandora on all of your Android devices (making sure to sign back in with the correct email address and password on each) so that all of your devices are signed into the same account.
I hope this is helpful, but please let us know if you have any more questions or concerns.