How to claim refund in cgst as it is not adjustable against sgst

My company in purchase material from other state and selling in Maharashtra..

So I have to pay sgst in full without any set off can't be adjustable of IGST.

I have to pay SGST in every month and my eligible ITC is against IGST purchase is always remain unclaimed

in every month. 

So how do I claim this ITC? is there is any simple way to claim this IGST Amount under gst law.