I would continue to use the cards as you are, as inactivity can lead many institutions to put your card in their "inactive" state thus not reporting history to the bureaus. As far as the department store, contact their CC department, and explain your situation and ask that they report the correct information to your bureau as the payment was made and the contract (you signed when you got the card to pay on time etc etc) was fullfilled. The error came on their side when you sent in a change of address etc.
Just be polite (it works wonders) and don't get frustrated and simply explain, I mailed in a change of address, it wasn't sent to my new address and I paid the amount due when I finally received my bill. I need to have an amendment to my report filed with the credit bureaus as this was an error in your billing system not by my negligence. If the first person you talk to isn't receptive simply ask politely to speak to a supervisor and repeat. Eventually you will get to someone who will have some common sense and will amend your records. Keep in mind it can take up to 6 months for this to take effect so as a CYA, have them fax and mail you the ammendment paperwork as well and take it to your local reporting offices to ensure it is ammended properly.
Just remember to stay calm and respectful the whole time, any sense of frustration or anger and they have every right to just hang up on you getting you nowhere. Plus they will typically put a note on your file saying how rude and abusive you were so on and so forth pretty much eliminating any chance you have in the future of receiving help.
