We want to start up Pen (Ball Pen, Refl, Ink) Manufacturing Business. now we want to know HSN Code and rate of GST

Dear Sir,
We have done a mistake in filing GSTR-3B . We have by mistake shown ITC on Reverse Charge for the month of December '17 in december GSTR-3B and also in January'18 GSTR-3B but it is to be noted that the mistke is done in return but we have utlisiled ITC on reverse charge in Jan'18 only . We have not used the ITC twice . As a result our credit ledger showing extra ITC on portal .
My queation is that can we show that ITC shown twice as reversal in GSTR-3B return only for March'17 but will pay the actual gst for the month . It will reduce the extra credit reflecting in credit ledger on portal.
PLs advise

Dear Experts,
Can anyone kindly explain me as Does we need to mention the Financial Year in GST Invoice like (18-19/0001 or 0001/18-19 ) ?? In our firm we started billing series like 18190001,18190002 and 18190003 like this we run series till now for 18190010 if any problem may occur for it ?? kindly expain me .
Thanking You.

I am sales commission agent, so can i charged on GST for sales commission bill ?

dear sir,
i m cancelled gst registration on 02.03.2018,composition supplier. im also filed gstr 4 from july to dec 2017 ., but not filed jan,feb turnover gst return and not yet paid jan,feb month gst amount.
can i pay the tax and file this return for 4q. give solution
reason below 20 lakhs turnover. but still i had not received an cancellation order and/or any communication,

What is GST Deemed Credit ? and how it is calculate ? Section (140(3)

We have submitted wrong 18% GST rate on Govt. works contract in GSTR3B of Sep-17 & Oct-17. But, we have correctly filed GSTR 1 for both these months with 12% rate. Now how do we get difference of 6% from Govt. Now only 1 GSTR 3B yet to file which is for Mar-18. So in which column we have to mention this difference of 6%. Please guide.

dear sir, i did not shown itc in form 3b for december month, but can i add the above itc in apr month gstrin 3b,
give a solution

We are wholesaler registered under GST. We need two cargo vans (ECO) for supply of our goods in Delhi / NCR on daily rental basis. VAN owners is not registered under GST. I have to know is there GST payable by us under RCM ? If yes, at which rate 18 or 5 ?

Can CA inter student file the itr and gst returns of their clients