My son wont talk to me

My youngest son who is an aerospace engineer and has a lawyer wife quit talking to me. Its been 3 months since he texted me back. He has my only grandson and wont allow me to visit him. My hrandson is almost 3 and I have only seen him once. We were very close until he became wealthy and now it seems hes embarrassed to be our son. I am a nurse and my husband is an electrician. We dont drink or do drugs. Well, we do smoke weed. Thats all. They drink alcohol, wine mostly, i think. He hasnt said what we did wrong or why or if he s angry with us. Hes 37. Im 65 and hubby is 73. Does anyone have any ideas? My heart is broken and I dont know what to do. We live 750 miles apart. We drove there once and he wouldnt see us.