gst number not given when he purchase

Mynampati Suresh (70 Points)

31 March 2018  
dear sir,

my client having gst number from september 17 but he did not give gst number when he purchase of the material, only given pan number and not issues any sales invoice also , commodity of medicine , small scale business, direct sales to consumer. now all returns is pending turnover below 20 laks .

pl suggest ,.