An ex partner of mine could stop talking for 2-3 days over micro aggressions she'd initiated.
Get rid.
I agree with Harry Wilson and his tackle.
Dump them but don't do it by text.
A dramatic approach is needed to hammer home the point. If you can't sing the dumping in a loud operatic voice your self, hire the bloke from the Go Compare Ads. Or an aeroplane with a message attached.
Not one of those roadside banners though with 'You're chucked' written on it - that has no class.
Maybe do a poll to find out the best way to do the dumping. And afterwards don't let them convince you that you were wrong about that.