Paid for someone else to a Premium user

[Bazzilla1]

Hi! I was upgrading my apotify account to preimum on my iphone, so entered my bank details etc but then realised there was someone else logged in to my account. no idea who this person is but i have just paid for them to be a premium user. I have tried to cancel the subscription but now it is asking for the users password. how come they are logged on and how can i cancel the subscription i gave them? thank you!!!