Wrong adjustment of refund against already paid demand

Dear all

I received a demand notice for AY 2010-11 which I paid next day online.

After about two months I received intimation u/s 143(1) for AY 2011-12 determining my refund but adjusting against the demand for AY 2010-11 which I had already paid and is visible in my 26AS.

While it appears that a rectification application should be filed , on website I could not find an option taking care of such type of mistake.

What should I do ? Please help.

Ashok Garg