That's very odd.

If someone wants to call my kids (now, or any time really ... this will still apply until they're 35 and have their own mobile phones!) they can do it on the home line, and even then it's not open slather for how much time they can use the line for.

Definitely his issue, not yours love.

And as others have suggested, if they call back again, I would simply say that this is Franny's mother's phone, and please don't call for Franny on this line. Ta taa.