If a firm does not come within new gst limit, can they not charge gst?

Arun (Business) (81 Points)

25 February 2019  

When GST came into effect, the limit was 20L and a firm has registered under GST and supplied bills with GST

Now the limit raised to 40 lakhs and firm total sales is below this. 

So can invoices be raised without GST going forward? And GST can be cancelled? 

Pls help understand this...