If you are physically able to pick up a phone, call the person and ask if it’s ok for you to use his service. If he says yes, use it. If he says no and you still use it, then all the halachic discourses in the world will put you at best in the category of naval birshus hatorah.
If you don’t pick up the phone then you are already at best a naval birshus hatorah. Is that what your yiddishkeit is all about? Relying on a possible halchic technicality to do something you know should not be done?