okay:

I deleted the app completely and signed into the account I am now using. I downloaded the app and authorized the account so it could be installed back onto my iPod. First thing scared me when it said I had 0 characters (but eventually it appeared when I clicked on the realm I previously played on and it appeared). Next thing I was worried that I would have to re-buy the previous campaign, but I didn't have to. I went ahead and tried to buy the next campaign and wallah! it works!

Thanks so much :]