Who is the RTA/registrar for SGB?, is it CDSL or RBI. How do we contact them if I have not received interest payments?
For SGBs, CDSL & NSDL act as RTAs, so you can write to them. You can write to CDSL from here and NSDL here.
The interest is paid out every 6 months from the date of issue of the bond. The date of issue can be found here.