Thanks for your advice and help again everyone, it does help.

UPDATE: (again!)

Ok, so I blocked her a few days ago and just last night I've had two text messages from a number I didn't recognise and it was her (again) asking why I'm not talking to her?

Seriously, it looks like she's went and bought a new SIM Card so that she can text me and now I've had to block that too!

My ex is now proving herself to be unstable in my opinion and it is starting to annoy me.

I will continue to not respond and block but I just don't understand why she wants to maintain contact when I told her we are done? Of course she knows I'm very depressed and hurt at her actions which led me to end the relationship but talk about kicking a man when he's down!