Hi..
Was the money received in foreign currency?
If we can classify it as export of services, we can claim the refund of IGST paid. The foreign company has paid it since you are not registered.
However, as an exporter of services, it is mandatory for you to get registered under GST. Then, IGST has to be paid by you first and then only the refund can be claimed.
We can assist you with registration and return filling.