I think the case is bit complex. So I have no choice rather to pay them fine before the discount period is over. Otherwise it's gonna affect my credit history.
So what makes this case complex ? It is easy; you mistakenly turned left, saw the CAZ sign, stopped then U-turned using the triangular traffic island and rejoined your original route. At no time did you enter the CAZ.
There is
no possibility of any affect on your credit history; put that out of your mind
now. Of course councils will browbeat you and intimidate you by saying they will take the matter to the county court if you don't pay, but they are bluffing. There is only ONE "court" that they HAVE to use called the Traffic Enforcement Centre that is there to register PCN debts. It has no court rooms or judges, and no CCJs result. A council can, once a PCN debt is registered, instruct bailiffs to collect the debt.
If you now take Birmingham to the adjudicators,
as is your absolute right in law, the PCN penalty is the maximum you are liable to pay if you lose. If you do lose, and then fail to pay after that, then the council can register the debt as above and get bailiffs to collect it.
But it's your money so pay-up if you want to.