I had a look at their enforcement policy on their website, as shown on the PCN. Look for the "Parking Services - Civil Parking Enforcement Protocol"
It is not very encouraging for your circumstances as it states in 3.28 Pay and display: -
Pay by Phone - motorists in Kettering who claim that they used pay by phone will need to show or provide a receipt from the Pay by Phone company and the PCN will usually be cancelled. PCN’s issued as a result of the motorist selecting an incorrect location code or inputting their vehicle registration number incorrectly will not usually be cancelled. (my underline)
However, don't be put off submitting a challenge, being very careful to not be confrontational, as they do use the word 'usually'.
