Interest on Tax Liability Difference between GSTR1 and 3B

Dear Experts

We have correctly filed GSTR1 of March 2018 showing tax liability of say Rs. 1 Lac

but at the time of filling GSTR3B we have mistakenly written tax liability of 10K instead of 1 Lacs
and in case of ITC also
we have mistakenly written 12k instead of actual ITC of Rs. 1.2 Lac as per GSTR2A.

and later on we have rectified this mistake in next GSTR3B of April 2018 where no payment made through cash ledger as there is sufficient balance in credit ledger.

now we have received notice u/s 50(1) from dept for payment of Interest on delay in discharge of liability.

our balance in electronic credit ledger as on 28 February 2018 is 70k

kindly suggest.