stayed on for 2 weeks and my phone bill was...."
Doesn't take two weeks. Back in the early 1970s a classmate called his brother in Belgium (I have no idea why his brother chose Belgium for his year abroad, but there it is), talked for a while, then both left their phones off hook as they went about their days, chatting again on and off. After 24 hours and a few minutes, they hung up. When the bill came, originating brother (in California) protested to The Phone Company that this was clearly a fault in their billing system as "Who would call Belgium for a whole day?". He agreed that he had made a "few minute" call, but not recall precisely how long. They removed the entire charge and I assume had some poor technician fruitlessly chasing down the "real cause".
All of which has nothing to do with mobile cameras, but as an illustration that "weird stuff happens" (sometimes on purpose), and has been for many years. If you have ever lent out a physical key to anybody, you should assume they made a copy and act appropriately (which may mean just get on with life) Your (and only your) task is to decide what is appropriate. (I use a camera-less flip phone with a removable battery, but that's me)