Don't take it too personally though I know is a tough ask, some new parents now ask for grandparents to give them time to bond with the baby before visiting. Try to send a nice care package when the get home - as Cossy has said if it is the UK and a straightfoward birth they could be out in 24 hours - order some nice bits from M&S or Waitrose, nice soups, lovely artisan bread, luxury biccies, tasty cheese and snacks etc., they will be glad of it in those first few frenetic days.
And keep contact via text or whatsapp rather than phoning for now, asking how things are going and sending lots of love and supportive messages.
Am pretty sure they will be asking you to visit soon and you will get to hold your gorgeous new grandchild.
Congrats and all the best xxx