€70 Racket: Charged for "excess weight" despite SMS offer for free checked cabin bag

I just had an infuriating experience at Paris CDG on a flight to Athens. I want to share this so others don't fall into the same trap.

Before the flight, I received an SMS from Air France stating the flight was full and 'inviting' me to check my cabin bag for free (up to 12kg). Once at the airport, I asked an agent if this was mandatory; they told me: 'It’s up to you, no obligation.'

Here is where the trap closes: By proceeding toward security/gate, I was funneled into a mandatory weighing station. They weighed my combined luggage (carry-on + personal item), which totaled 14.5kg. They handed me a slip with the weight and sent me straight to the counter.

At the counter, it felt like a shakedown. They demanded €70 for being over the limit. When I showed them the SMS promising a free checked bag for my carry-on (which alone was only 9.5kg—well within their 12kg 'free' offer), they flat out refused to honor it. They claimed that since the total exceeded standard cabin limits, the SMS offer was void.