Sorry to butt in here - but I had a very similar issue at the Forest Hill Station which I am STILL trying to get resolved. I was charged for my 7 day travelcard on the Monday Morning (i've got the receipt from the purchase etc), went to work and everything seemed fine.

However when I tried to get through the ticket barrier at St James' Park Station, my card didn;t work. I took it to the counter and asked the sales person to check it - which he did (grudgingly) and then informed me there was no travelcard on my card. I showed him my receipt from the morning - he said London Underground couldn't do anything about it and that I had to go back to Forest HIll and get them to sort it out. Yes, I did point out to him (he was about as thick as most of the LU workers) that I clearly couldn;t get back to Forest Hill to sort it out, because the travelcard did not work. I ended up having to buy a new one (so another £30). Only to find out that I STILL couldn't get through because my PAYG balance had now dropped into the negative - I then had to add more cash to my PAYG to take it back into the positive. Got to Forest hill only to have the useless Paul Whitehouse lookalike guy tell me it had nothing to do with London Overground, and that I would have to go to Oyster...now I know the staff at Forest Hill are absolutely rubbish at their job, and I know they should all probably be fired immediately, but I did think they'd at least be able to handle a simple issue like this - they can't so don't ever bother with them - they suck in their entirety.

I contacted Oyster who told me I had to go to London Underground to get a refund - now this wasn't a purchase I no longer wanted, this was THEIR mistake - and they told me I had to fill out some forms and send them to the head office - the head office is 120 ft from my work - but you can't just drop it in, you have to send it through the post. Now I'm continuing my claim wiht them and racking up a fair penny in all my fees for phone calls, postage, interest (which is already several times the amount of the ticket price) etc...and to compound matters further - exactly the same thing, with so far the same results, has JUST happened to my wife (this Tuesday past).

My advice is get a receipt everytime - or top up online - you cannot trust the machines at the station in HHP or Forest Hill, and I don't know about the staff at HHP but my experience of the staff at Forest HIll is that they are absolutely, utterly and without exception, useless no brain morons who seem to have been given their jobs because someone had to give them something to do or risk the union complaint. They'll spend all morning telling you to "get back behind the yellow line" (I never do) but they can't sort out an Oyster card, give you directions or, heaven forbid - tell you a train has been cancelled!!

rant over - but I do feel for you guys