See as per the rules of UGC, you can't pursue two full time courses at the same time. So you have to complete you BA Economics either then start your Diploma or the vice versa. But both can't be carried on simultaneously.

Now if you are interested in the Special education then you can self educate yourself through online sources and other ways and after your completion of the BA you can pursue it.

I hope my answer helps. All the very best for your future endeavors!