Hi Lancer,
It sounds to me like a common problem, especially as they knew what you were going to say to begin with.
I doubt they will take this any further, and just take this off.
However, you really want to settle the account before you set off leaving the UK for good. If you ever wanted to come back, it would be a shame if £50.00 and several CCJ/Defaults because of it, landed you unable to get credit in the future.
They wont chase you abroad for £50 but they can still impair your UK credit.
PS. you going anywhere nice? I'm thinking about leaving too... UK is getting ridiculous to live in. Can't say this, Can't do that, How much?!?! etc!