Old clients may continue to phone the number.
They may well do, but it does seem a really odd thing to do.
Hasn't she made enough from the business without trying to extract the last few pennies from her phone?
Apart from the occasional very rare examples, such as yourself, Dani, Holly, Louise etc, I think that the typical prostitute has a very extreme selfish, psychopathic and manipulative personality. Which means about 99.99% of them. They really are a breed apart and totally untrustworthy.
I unwittingly once shared an apartment with one for a while. She was a very intelligent (and by very, I mean exceptionally bright, I've never met anyone else with the intellect she has), and an engaging and interesting person. But boy o boy the things she did don't bear repeating here, and the two faced way she treated many of her clients was utterly appalling. I put up with it for a while (never went anywhere near her in the biblical sense), because she was actually really good company as a friend and flat mate, although also a pathological liar, and bullshitter extraordinaire. They get away with it all the time and it becomes normal to them. However she really rubbed my nose in it one day and I realised what a total psychopath she is. Since then, now I know what to look out for I have seen the same traits in every single one I encounter.
The lesson is that you have to be totally untrusting and on your guard ALL the time, and with every single one of them. They are totally different from ordinary women.
Selling a phone already full of punters numbers! Whatever next?