I’ll try and be more helpful.
You are right about the 14 day/registered keeper rule, and also right about the reason there is the 14 day limit.
Are there any records of who has the car on a particular day, or do you have a work diary/secretary so you can check what you were doing. The registered keeper is obliged to name the driver of a car at the time of an alleged offence when required to do so under Section 172 RTA, so I’d be asking whoever is responsible for vehicle records why they thought that was you.
Just playing devil’s advocate now, but if one had exceeded the speed limit for a good/justifiable/mitigating reason, would one not have remembered? Perhaps not if it’s a daily route.
I’m assuming that if you have received it through the post, your company have already responded and named you as the driver?