Ok so the dialler can make any number it wishes appear. That's illegal but many crappy sales operations are illegal in their actions. A few years ago my wife was having the same problem all day and night. I made it a police mater and they traced the calls and solved the problem. In her case it was actually a business run by students out of keele university!! After police intervention it stopped in an instant.
Interesting as I was thinking of the possibility of getting the police involved for harassment everyday. But I thought the police would not be in the slightest interested.
She now has that App on her phone blocking the number range. Hopefully it will stop now.