Ds is 15 and his father and I broke up whilst I was pregnant (he went off with someone else) and he moved abroad when ds was 3. I've always been welcoming to ds's grandparents as I thought it important for him to know all of his family, not just my side.
Ds and I moved house a couple of years ago to be closer to ds's school (his father had also stopped paying maintenance so we needed to cut costs as it was costing £150 a week just to get to school). We moved 15 miles away from our old house, I don't drive but she does so it's not far for her to come but she hasn't come to see us at all, despite her having siblings three miles away. She hasn't called (my phone number's been the same for 16 years), she doesn't return my calls or answer my text messages, she hasn't emailed (she has my email address, I've emailed her to let her know how ds is and she's never replied so I gave up after 6 months), and the last letter she sent was attached with a newspaper article about funding for a boarding school (he's at a private day school which I pay for without help from his father, she's spent 11 years before this telling me to move him to various schools around where she lives). We've been back to the old town a couple of times and have met up with her there but there's no other reason for us to go and I don't really have the time to do this as I work weekends and during the week, I also have MS so am not always able to run around on my days off.
She's quite hard work when we do see her, she'll ignore ds and will interrupt him to talk about random things when he's trying to talk to her or me, she once left my house in a sulk because he didn't want to give her the book that he was reading until he'd finished it (he was 5), she also went into ds's primary unannounced at lunch time and asked for a copy of his school reports because I didn't give her any information about how he was doing and told the head that I was jealous that his father had just married. There's other things too.
It was ds's birthday yesterday and she's sent him a card, saying how much she misses him and how she only has old pictures of him which she looks at all the time, and she doesn't know what he looks like so she only has these 
. She's said that she'll send him a gift when he gets in touch as she doesn't know if she has the right address for us, despite sending us cards/letters over the past 2 years and us trying to keep in touch , "a letter would be good so I can read it and think of you".
I'm quite pissed off to be honest. I'm happy she's sent ds a card and she's told him that she's thinking of him, but it feels so manipulative to say I'll only send you a present if you write to me.
Any ideas? 