Question about seat classes and upgrades.

Hi peeps,
I bought a return flight to BOS out on July 1st and return July 8th.
Outbound is UC (Seat class Z)
Return is Eco (seat class X)
I noticed for about a week after I had bought this ticket on-line I noticed that I could upgrade my seat on the way back to either PE or UC on-line, At the time I did not have the funds to do so. But I do now, However the option to upgrade on-line is now longer there, So I decided to call the Upper class reservations team, I only had to wait less then a minute on hold, and got through to a really helpful lady, "you want to upgrade on the way back sure no problem that will be £199, oh wait a minute sorry with your fare class on the way back I cant do the upgrade im so sorry"
When I asked why I cant upgrade now, but had the option to for about the first week when i bought the ticket she did not know why!
My Question is:
1) How come i had the chance to upgrade on-line for around a week and then the option disappeared.
2) I'm not in the bottom fare class for eco as far as I can see, and there are spare seats in PE, why cant I upgrade?
Many thanks
Mike
I bought a return flight to BOS out on July 1st and return July 8th.
Outbound is UC (Seat class Z)
Return is Eco (seat class X)
I noticed for about a week after I had bought this ticket on-line I noticed that I could upgrade my seat on the way back to either PE or UC on-line, At the time I did not have the funds to do so. But I do now, However the option to upgrade on-line is now longer there, So I decided to call the Upper class reservations team, I only had to wait less then a minute on hold, and got through to a really helpful lady, "you want to upgrade on the way back sure no problem that will be £199, oh wait a minute sorry with your fare class on the way back I cant do the upgrade im so sorry"
When I asked why I cant upgrade now, but had the option to for about the first week when i bought the ticket she did not know why!
My Question is:
1) How come i had the chance to upgrade on-line for around a week and then the option disappeared.
2) I'm not in the bottom fare class for eco as far as I can see, and there are spare seats in PE, why cant I upgrade?
Many thanks
Mike