Renting of cab under GST

hello Friends,

I have one question related to GST.

ABC an individual providing 2 services such as renting of cab and contruction services.But during GST registration they registered only for contruction service.
Further ABC providing renting of cab services to body corporate.And a body corporate pay a GST under RCM.

Furthermore ABC make an invoice by showing the GST no. but they not charge GST on his invoice in case of renting of cab to body corporate.

Plz suggest ABC make a fraud transaction or not by not showing their 2 service. Or ABC can do so.