Please post the back of the PCN so we can look for errors in the "small print".
It might be worth submitting reps on a grovelling basis, saying that you were staying at your parents and had not realised the month was now May, (the PCN is dated 1st May), so scratched-out the wrong month and ask that on this ocasion the PCN be cancelled. However the hardest of hard hearts are found in council parking departments, so don't expect too much, but you never know.