Parties GST No. Cancelled.

Do not cancel invs

but amend b2b to b2c

You cannot cancel these invoices in this case now you can Amend these invoice from B2B to B2C. but in the other hand please contact with you customer if he wants to continue his business as Un-Registered Taxpayer under GST then you can.

If the Customer GST Number Cancelled and he close his business then its your choice how to handle with him for the payment purpose but you cannot cancel the invoices, in other case if you want to nullify the Account then you can issue credit notes against those invoices in GSTR-1