This is a classic case of your ex wanting to keep his options open. It also sounds as if you haven’t given him the ego boost he expected, by begging him to come back to you. So well done you!
Despite the situation, you have adopted a mature approach and explained why you don’t want any contact with him at this time. You don’t owe him any further explanation, so don’t respond to these wholly unnecessary text messages.
He is simply looking to weaken your resolve and it is vital that you don’t allow him to manipulate you any further. Re-read the article for guidance and block his phone number. It is also advisable to block him on social media sites also.