Interest Calculation For GST Payment.

The Service Provider failed to pay the GST (10350+10350)20700/ before the due date (i.e)20th August 19.He Noticed the error only Now.As Per Sec 50(2) interest on delay (Aug 19 to Feb 20) of 7 Months works out to Rs.26082/-.Please let me know whether my interest working of Rs.26082/-is correct.If so shall I have to pay the aggregate amount (20700+26082)Rs.46782/- or the restricted amount of Rs.20700/-Pleas Advise.