Purchases and being made without my consent. Devices streaming on my account that I don’t reconize

I noticed over the weekend I had movies on my bill that I never watched. One movie was ordered 6 times at $3.99 a pop! With a total of over 15 movies rented. Let’s just say I’m not happy!! I’ve been doing some investigating and was able to catch the person in the act last night. I narrowed it down to someone renting them through my Stream app. (EVEN AFTER I CHANGED MY XFINITY USERNAME/PASSWORD)
I wasn’t able to stop the device. The device name was “LGE LG-SP320”. I’m reaching out to see if anyone else had this happen to them and what should I do? I’m thinking I might have to disconnect all my Xfinity services(tv, internet, phone) if I can’t figure this out. I can’t afford all these movies that I didn’t watch. Please help!!