A challenge should be made by the driver because they know what they did and why. Your draft is written in the first person, but this person isn't you.
Who is going to submit the challenge?
The 14-day risk-free(as regards the discount) period ends on 8 Nov. I suggest a challenge is submitted by then.
IMO, the reference to and reliance upon the Equality Act is misplaced, there are more places reserved to BB holders than you could shake a stick at.
IMO, simply state that 'I' as in driver saw the parking place marked with a clear ISO wheelchair symbol and parked there. The bay was also marked with a symbol used to indicate that vehicle charging facilities are also available but I did not interpret this to mean that the bay was reserved for the dual use of charging electric vehicles also displaying a BB.
The PCN clearly shows that the CEO, and presumably the authority, believe that this bay is designated solely for this dual use. However, there is no reference to this on the Ts and Cs which are clearly publicised on the car park noticeboards neither, crucially, in the traffic order for the car park.
I appreciate that this order wasn't made by Somerset Council but by one of the predecessor authorities subsumed within Somerset unitary, but until you change its provisions it applies. And as you know, there are no references to dual use, if fact 'electric vehicle' isn't even in the Definitions and Interpretation section.
In summary:
I parked in a bay which was marked with the ISO symbol for disabled;
I noticed the presence of another symbol used for indicating electric vehicles;
I had no reason to believe that these were intended to be read together(the ISO symbol cannot be caveated) and therefore interpreted the use as 'either/or';
There is nothing in the Ts and Cs or in the order which provides that these are to be read as limiting conditions in combination.
I therefore submit that the contravention did not occur.