Charged Extra for EasyJet Flight Despite Prepayment – Requesting Refund

On EasyJet flight EJU7204 from Manchester to Barcelona on November 16, 2024, I paid €26 in advance for my son's cabin bag. However, at the gate, they charged an additional €48, despite the bag being within the 8 kg limit. I expect a full refund for the extra charge. If this issue isn’t resolved, I will escalate my complaint to Star Alliance. Please address this immediately.