Just to let you know how real telegram users see this ( speaking in my experience but I'm sure others share my oppinion ) . Whenever I get automatically joined to another group which I didn't sign-up for , I ignore all content on that channel , and go straight for the report spam button and block the group , regardless if your group is legitimate or no.

Instead of you wasting money on this shitty service , that will get your group countless of reports , why don't you use that money to advertise your group a little ? Or better yet make an announcement thread here on bitcointalk , describe your group , and what your project is about , and I'm quite sure you'll get people to join your group.