CA issues - pls advise!!

[Toga101]

What is the name of your state?What is the name of your state? California

Can anyone offer advice? I'll try to make it brief:
In Nov 04, a Collection Agency sent me a letter for an outstanding phone bill from June 04 (closing balance after I moved out of an apt). I called the phone co to verify and just went ahead and paid it online the same day I rcvd the letter... because I was moving, it seemed legit. I checked my Credit Report two days after making payment, and it was all clear.

Well, I checked my CR again yesterday and the CA ended up posting the item. I have a feeling I've been screwed... but is there anything I can do to have this removed?? I mean, I paid the CA immediately (maybe bad idea?). Also, the credit report has bad info (it says i've been delinquent since 7/03). Finally, this is the first notice I've rcvd for this EVER (neither the phone co or CA contacted me before).

Can the CA possibly just remove it? I know it's a big stretch, but any advice would be very much appreciated. Thanks! (and btw you guys are great, i read through most of the postings before i wrote this)