26-09-2014 09:01 - edited 26-09-2014 09:02
You will continue to have the discount until you change contract. It only expires when you upgrade to a new contract.
Therefore, if you do nothing you will continue to enjoy 50% off the airtime, with no expiry date.
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)