more than two years waiting on INSEE/CNAV/SANDIA...who to contact about the delay?

Geraldine, the answer given on the link you provide is useless. I have been calling the English support line for years, and they do not have access to the file details like someone in a CPAM office (...and I've been literally turned away at the CPAM outer door in Nice because I didn't speak french)...[oh, and did I mention how the Antibes office refused to let the English help line do translations between us over the phone?]

That answer also has no information on how to escalate the issue for cases that are taking too long, nor even a definition of "taking too long" whereby CPAM acknowledges the need for escalation.