if you give them both codes, they will then be able to use the service YOU pay for free of charge, you may have a limit on usage and if you do anything over your agreed contract will be charged to you and you could end up with an unexpected bill you cannot see over, no, don;t do it, tell them you do not know the codes as it was set up for you and if the code is on the top of the router on a sticker go and remove it and stick it on the bottom of your freeview box or some where else safe as they may suggest they come in and look at the box for the code, cheeky beggars