Just sharing this as it happened to me a while back and I've noticed lots of Charged Twice posts.
If you tether a tablet or device to another phone, or mifi, homefi, whatever - anything that has its own SIM card.
Subscribing to Spotify / renewing on your main device, can trigger a charge to happen on the wifi device too. This is because devices with SIM cards are capable of mobile payments, which is controlled by your phone provider.
So for instance, we use a 4G router / homefi setup, with a SIM card. I had to contact the provider of that SIM card and disable all mobile payments.
That provider was running a promotion on Spotify subscriptions, and picked up my renewal as a new account. So I was charged twice. Spotify did resolve it and refund me. Thanks guys.
Anyway - just sharing.