While I doubt neither the veracity of your claim nor your reaction to Gandi's actions (if such a situation happened to me, I would certainly not want to give a company my business going forward), I have had a very different experience with them: all of my queries to Gandi support have received prompt, relevant replies that addressed my issue.
Also, ny domain registered with Gandi can be renewed by any Gandi handle. In the event that you're having trouble accessing the handle that owns a domain or otherwise cannot renew it normally, you can create a new handle and use that to renew the domain. See https://wiki.gandi.net/en/domains/renew and https://www.gandi.net/domain/renew?lang=en for details.
I'm not sure if their "any handle can renew any domain" policy/system existed at the time of your situation, but it should prevent similar issues from occurring today.
Also, ny domain registered with Gandi can be renewed by any Gandi handle. In the event that you're having trouble accessing the handle that owns a domain or otherwise cannot renew it normally, you can create a new handle and use that to renew the domain. See https://wiki.gandi.net/en/domains/renew and https://www.gandi.net/domain/renew?lang=en for details.
I'm not sure if their "any handle can renew any domain" policy/system existed at the time of your situation, but it should prevent similar issues from occurring today.