who's right?

Jonny17291:
He is adamant that as soon as that tacho goes over 12 hours it’s now considered a 15 but I’m sure its 13 hours. 11 - 24 = 13 hours

You are right, he is wrong. Any 24hr tacho period where you are on duty in excess of 13hrs (excepting the aforementioned split rest period of at least 3hrs continuous during that shift) is automatically a reduced rest period.
The old hands can be the worst when it comes to interpretation of the rules, I’ve personally witnessed one arguing with a CPC instructor till he was blue in the face that you could legally exceed a 15hr shift with use of POA as it freezes the clock in his words