Sons family ?

So it’s been almost a year & 5 Months since I heard about my sons family or that they have contacted me about him. And today I received a message from his grandma asking how hesdoing . His father is not in the picture and doesn’t seem to cares. My son is 5 years old. I didn’t reply to her cause i don’t even know what to say. They stopped contacting me in April 2017.

Don’t know what to do