I think there may be a flaw in the wording of the PCN.
The law requires the PCN to state (amongst other things):
"
(iii)that the penalty charge must be paid before the end of the period of 28 days beginning with the date of the notice;
(iv)that if the penalty charge is paid before the end of the period of 14 days beginning with the date of the notice, the amount of the penalty charge will be reduced by the specified proportion;
(v)that, if the penalty charge is not paid before the end of the 28 day period, an increased charge may be payable;"
Clearly, in that context, the 28 date period in part (v) is 28 days beginning with the date of the notice.
Your PCN states "If the penalty charge is not paid before the end of the period of 28 days beginning with the date of service of the Notice, an increased charge of £240.00 (less money paid) may be payable".
Date of service is different to the date of the notice (presumed to be 2 business days different by law). As such the PCN does not comply with the legal requirements and ought to be unenforceable.
@Hippocrates is the go to member when it comes to technical deficiencies - see what he thinks.