Sainsbury’s complaint: Unable to log in to their webpage for 2 months now

I’ve been using SAINSBURYS webpage to order groceries for many years. When I tried to do my October shop, after Logging in they presented a further Secure level. They said that they had sent an email 6-figure code to my Inbox. No such thing arrived! On the first and second occasions I called their helpline. It sounded like in India [as opposed to the usual UK-based]. The poor operator tried everything, even giving me a temporary loginpassword. No good, as this Link didn’t arrive in my Inbox either.
Emailing them is useless: first they ignored me, and the second time they wouldn’t accept any more messages as the facility was full.
It is all down to this 6-figure Security. Other firms use PIN SENTRY or a telephone link for added security. They must be losing a million quid in business because of a simple computer glitch. I had to keep complaining a few years ago because their webpage was unstable. Whatever intellectually challenged were running the tech side then wouldn’t or couldn’t correct it for ages. Kept blaming the User, the ISP, etc.