I speculate that you are up against the reality that Chase no longer owns your credit line. They likely securitized it, now it is owned by a trust, and Chase administers it. Once the line is zeroed out the terms of the trust may not allow it to be recreated. There may be a 30 day window while changes are processed, but if you haven't been using the card, and haven't been paying any interest, no one at Chase may be motivated to manually undo this.