Who looks after your GC now, when your DIL is working?
Is this person paid (ie are you upsetting an arrangement that's already in place)?
How many hours does she work?
How many days?
I think some of these replies are unnecessarily harsh, you are not being unreasonable (I always preferred to look after the GCs at my house) but your DIL has made her wishes clear, so I'd go along with them for now as most people recommend.
However, as she is not contacting you, you are in a difficult place. Why nor try a text asking her if she still wants you to come round on ???day as usual - and accept her decision even if she says No Thankyou.
You DO see him, some of us are not given even that opportunity, I see my son's children on birthdays and at Christmas, my DIL does not let me see them in between and if I call round she gets their coats and says they are going out, when its obvious they're not.
If she tells you she no longer needs your help you will have to accept it, and leave things as they are for at least a month.
But it doesn't look as though you'll get your wish until he's much older.
Sad, because you could be such an assert for her, she's a silly girl to be so pedantic.