Nah, don't worry m8, I'll let someone PM you that can use it as I just recently purchased a year of PS+ for my UK account but thanks and sorry you got screwed outta that additional week. My bet is it's locked that way to prevent people from stacking endless free trials onto their existing subs.
Please use the edit button instead of double posting, you know that. Please follow the rules, I've had to merge quite a few posts and its not the first time.
