I am not sure "sorting it" is that easy without asking other people to move. The "cock up" was caused by the friend asking to move seats. The lack of communication between you and your friend seems to be the problem. I'm glad the ticket office have agreed to deal with the problem but the next post we might see on here is from a disgruntled supporter who has had his season ticket reallocated to deal with a problem that was caused by somebody else. Probably the easiest solution would be to ask the person occupying the seat you want to swap with you.