Since I am not really into telegram, I just briefly checked:
- If you can manually log in in the bot and verify the sms code from your real account (or in your telegram app) then
- click on the group
-I could go through the list of users, scrape the usernames where applicable
-or click add to group, although only saw that on one bot account
- send a message, although I'd assume that you spam too much you get banned.
So not aware of any ready-made tool, if you want to hire someone to do this for you post in the hire a freelancer section. That way, only paid members can contact you and less of a chance of being scammed.
Good luck