I figure these gentlemen are either
a) clueless and just don't realize what they are doing,
b) have a serious mental problem, or
c really like you, and don't have the means or opportunity to see you as often as they want to.
I can almost understand why someone would drop you an email every 4-6 months because they are concerned that you might forget about them and have to go through screening again. Some of us just don't have enough opportunities to maintain references. But texting is ridiculous.
If you know how to use one of those websites that enables you to SMS text from your computer, you could maintain a sort of "formletter" outlining your policy and feelings with regard to these texts so you can send it when necessary without as much trouble. You've already done an excellent job expressing a very reasonable stance.