I think you did fine here. The truth is she could find you if she needed to. If she calls and gets finds out that your old number has been dicounted you can just tell her that the contract came up and you switched carriers. That's assuming it's done in the UK the way it's done in the US, where you get a phone number for a period of time until the contract you sign expires.
But truthfully your making great progress and you maintain such a positive attitude, you've grown by leaps and bounds since you first came here that I hate to see you start looking back. I think you making some tremendous positve advancements for yourself and you should not second guess it at this point about ANY choice you make that relates to your emotional well being and healing. Remember this no contact isn't to punish her or et back at her, it's for you and you alone. It may bring it's moments of doubt and difficultiy but it's the only way to really make the change and allow the acceptance that it's over.
I fully support this descion and quite frankly if she needs to contact you make her work for just the contact. She emotionally let herself out of the relationship before she physically left so you are under no obligation to be there in a physical sense if she tries to contact you.