Help 'WA_PUSH_SI!' keep showing up in my texts!

I keep finding 'WA_PUSH_SI!' as a text sender in my texts, but it is blank and I cannot keep it deleted. I will attempt to delete it once and it does not disappear. I attempt to delete it a second time and it shows up as Anonymous in stead of 'WA_PUSH_SI!' . Most times it will still not delete. When I delete multiple messages along with it, it will disappear, but within a couple of days, it reappears. Help please.