cancel one account and use the other one. dont contact adsense support as they will probably ban both accounts. if you dont have any ads created for one accont and if you cancel it before making any earning, they will probably not know that you ever had 2 accounts.
May I add one more 2cents ... ? I have had 3 accounts with Google over the years simply because that is how many sites/businesses i worked for in that period of time. And - there is no problem to having multiple accounts, if your IP address is different for each one. For instance, if you don't want to use your old one, then just don't use it on your existing PC. If you already have, then contact your Internet Service Provider and ask them to change your IP address. Then use the adsense account that you want with no problems and keep the old one if you need to. Google has a dozen different silly ways of doing things and if you have worked there you will notice that there is so much anal concepts of secure accounts that actually not much is secure when you look at that much data. The servers there are very high powered servers and they are all (every single one) custom made internally - and there is so much datacenter caching going on there that they just can't monitor things the way they want to. There is only so much automation that humans can manage and set policies for. Webmaster http://www.writersviews.com