Do homeless hostels in London charge people money?

As it says in the title i often come across people begging on the overground for money so they can get a hostel for the night. But when i google it it says that hostels are free and you shouldn't give the people money, this is a statement which is also echoed by tfl.

So what is it?

Do they cost money? or is it that a certain kind of the ones they want to go to cost money?, its something which ive always been kinda curios to know

Thanks