Chomp SMS - Group Messaging

Good Morning, newbie here and Im hoping Ive picked the correct forum to post this on...

Ive downloaded Chomp SMS for my messages.
Basically I need to text a large group of people (100+) on a regular basis and Chomp seems to be the best application to do this.

All of the people I need to text have been linked to a group under contacts

However, when I click on create a message, and select the group as a whole, when I then go into the individual contacts which have been selected, a very large amount of those people haven't been selected

Through process of elimination, I think its linked to What's App. All of the contacts that aren't naturally selected by Chomp all seem to have two 'tabs' within my contacts as the Whats App has been linked to the individual contact.
Has anyone every come across this before and if so, have you found a solution?
Thanks in advance