email the chief cunstable
acpo.staff.office@south-wales.pnn.police.ukand ask what the hell they're playing at. Provide a map of where you had been legally riding and the location where you were given the warning.
btw you cannot appeal a S59 warning.
the powers are:
Where a constable in uniform has reasonable grounds for believing that a motor vehicle is being used on any occasion in a manner which—
(a)
contravenes section 3 or 34 of the Road Traffic Act 1988 (c. 52)(careless and inconsiderate driving and prohibition of off-road driving),
and(b)
is causing, or is likely to cause, alarm, distress or annoyance to members of the public,
even if they have cause to believe part A was commited, where's the cause for part B?