I need to make sure I'm running my cold sms to only mobile numbers. Do you know any cost effective phone validators that I can use?

I just started doing cold sms to contactors, but when they seem interested and I follow-up they never respond to my texts and when I try calling them, the calls don't go through. I am fairly new to cold sms and yes at least people seem interested but why aren't they responding?? How do I fix this? P.s - I've had these leads for a while and they aren't in a particular niche, I'm not sure if that may be contributing to the problem or not. Feel free to give me any helpful advice regarding this.