Q: i delete mail in junk box but keeps returning . Why?

I have a mc book air late 2014 13 inch 128 gb sdd. i have an ntl account gmail hot mail and virgin media plus another outlook account.

It is running the ox s 10.94 software. I don't want  to upgrade it yet.

Every time i delete horrible scamming junk mail the contents are deleted . But the emails are reloaded onto the system  back in the junk box i have emptied  why and how do  i fix this

Thanks