If the car was parked outside No 99, and the suspension covers 91-95, then the contravention did not occur.
So submit representations on those lines, and post up their reply when received.
Something on the lines of:
Dear Sirs
Pcn <PCN Number> dated <date> at High Road, Haringey
I deny liability for the above PCN on the grounds that the contravention did not occur. My car was parked outside No 99 but the parking suspension sign states that the suspension applies between Nos 91-95.
Yours faithfully
There is no need to put anything more, as this is an informal challenge.