I believe I am having the same issue where I took an upgrade in browser (which upon later inspection wasn't reflected in the confirmation email after being stung by unforeseen charges). I wasn't fortunate enough to have screenshots of the offer I selected as you have but I did have a customer service representative tell me that their system was in error, offered me a refund of my charges, and that an investigation was looking into the causes for me.
One month later and my next bill comes through, charges still on there, no refund. Having called up customer services again, they claim that free roaming was never included, but they do have record of a refund request being noted on my account. They then put me through to the upgrades team who tried to upsell me on contracts and handsets to restore free roaming for me but not as competative as offers I could find myself online from EE - at which point all remaining trust evaporated.
