ITC Revarsal

A company was taking continuous services from another company since 2016. and the company was booking the expenses as invoices were raised by the supplier. when the final settlement done in December 2017(GST Era) then company has reversed the expense by Rs.6 Lakh as the final settlement done in Rs.12 lakh only where company has earlier booked the expenses by 18 lakh and also taken service tax credit on the same. but now in December while reversing company has not reversed the ITC credit taken earlier. now wat will happen? is company required to reverse it?