When I was much younger, I had a childhood family friend. So this dude noticed that when his parents are making offerings, they tell the invisible spirits where they stay and they are here to make offerings.. Blah blah blah..
Being a dumb kid, he thought he would be clever to write their phone number and address on a piece of paper and burn it together with the incense paper (offerings).
Later that night, their phone rang and when his parents picked up the phone, it was some strange mumbling. Dismissing the thought that it was a prank call, they hung up. Five minutes later, the phone rang again and it was the mumbling. So the parents warned that they would "call police" if the prank calls were to continue.
Another five minutes later, the "prank call" came again and they decided to unplug the telephone cord. However, another five minutes later, the unplugged phone rang again. Realising it was a paranormal activity, they questioned my friend and the truth came to light. So they made another offering and asked not to be disturbed.
This is a true incident which happened more than twenty years ago. I have many other first-hand encounters you can ask me about when u buy me coffee.
Happy hungry ghost festival, everyone!