You've pretty much got nothing.
Driving offences (which are crime) are committed by flesh and blood people.
That the vehicle used might be registered to a business
does not make any difference to that.
You could well have court-elected the infringement when it first came in,
but you didn't.
Now, at Final Notice, the time available for you to choose that path
has almost certainly expired.
If it wasn't you driving (I note that you do say it was you),
then you could have nominated who the driver was (one of your employees, maybe?),
in which case they would have been liable for the fine,
but you didn't.
Now, the time to take that path, it it ever existed,
will have almost certainly expired.
Lawyer Tip: Do not ever nominate yourself as a driver if you were not.
"Taking the points" or "copping the fine" for somebody else... don't.
Lastly, I'm curious.... That's a big amount for single fine.
Was it one offence, or was it multiple infringements
(perhaps on a defective heavy vehicle)?