Do you have any other points?
I will need to ask other questions. Otherwise the answer will be wrong.
When did you pass your test?
Ok. What was the limit and what speed were you doing?
It depends how much risk you are prepared to bear in that case.
You could always refuse the offer of the fixed penalty and ask for a trial as indeed you were not speeding at that time.
However, the reality is that they will almost certainly find this at some point. When they do they will just amend the charge and then you would be left with no option but to plead and the problem of being liable for costs.
You may be lucky. They may forget to summons. That does happen sometimes. You cannot rely on it.
Alternatively though, you would only be offered the fixed penalty or the speed awareness course anyway. You don't have other points and you are not at risk of revocation under the new driver's scheme so there is a limited risk.
Contesting this is open t you but it is very high risk for fairly little gain.
Can I clarify anything for you?