If things would go wrong with WG i can block her number. So she couldn't call or text me. You can do it with Windows Phone but i'm sure Android and iOS have this feature too.
all she'd need to do is use another number, then another and so on or withhold her number and that would ring.
Next step you'd need to do is block all withheld or private numbers and numbers not in your contacts.
Now, this would stop a lot of companies, government departments and people like doctors getting hold of you. If you blocked all mobiles not in your contacts, then I'm also sure you'd miss some important calls.
Wgs can change their number daily. and I bet you'll never meet one with less than 3 numbers. sim cards are pennies if not free so the cost to change is minute and a tenner top up to a girl earning 1000s a week is painless.
Your Way out is change numbers (new contract), change via provider explaining nuisance calls or have a chat with the boys in blue.
This is all a headache I can do without