Did you ever log into your ad sense account at a public place - say a cafe or somewhere else and had forgotten to logout? Someone probably changed the profile details.
You can either change the profile details in your current ad sense account (log into your ad sense a/c, then click on the "wheel like symbol" on the top-right, just beside your email id. Now click on "Settings". Then on the "Personal Settings" page, do you see your name or someone else's? You make make changes if you wish to on this page.
Then on the last option "Site Management", check whether your blog's url is mentioned under the tab "Owned" (it should be because you had already enabled ad sense for your blog). If not, then add your blog's url in the given box and save.
Then go back to the home page and click on "payments" on the right. Choose the 3rd option - "payment settings". There you will be asked to add your payment mode - whether wire transfer to your bank or through cheques. (Wire transfer is simple and takes about a week for the money to get transferred to your bank a/c).
On the "payment settings" page, you can then enter in your bank a/c holder's name, a/c no, IFSC code of that branch of your bank, its SWIFT code (you will have to contact your bank to know it if you aren't able to find it from the internet. I will suggest you to not take a chance and better collect the info from your bank) and save it.
Now after you have made all these changes, log out and then change the password of that same google account (your gmail passwrd will also change with it simultaneously), so as to foil anyone's attempt to get into your ad sense /ac.