Can we change the outward invoices relating to 2018-19 now

Hi Everyone,
we are in the business of construction.
we have raised some invoices in 2018-19 for which we have paid the respective gst for the same and sent those invoices to clients..
but now clients are claiming that we had not received the invoices and didn't took gst input and asking us to raise the same invoices this year so that they will pay the invoice amount and claim the input..
we are unable to ask them strictly because of risk of losing the client..
kindly suggest what can we do..
can we raise the credit notes for the invoices raised in 2018-19 now and show them in annual return???.
or there is any other alternative..
please help me.
thanks in advance......