Regarding gst invoice did not reflect in the portal

We purchased some stationery items from a company  and got a GST Invoice. . But we noticed that IGST amount  did not reflect in the GST portal.

Then we asked seller why it was not reflected they replied that our GST no did not register with them. But our GST Number clearly mentioned in the invoice but they told we did not register with them. So my question is how i get input from them or there are any law in GST that that we show them or what to do? Please suggest.