gta service

no, GTA liable to pay Gst if registered 5% or 12% as may be

if GTA is also unregistered then nobody pay tax

GTA(RD or URD) service to UNREGISTERED person is exempted.
Please check notification 32/2017 central tax dated 13-Oct-2017 Sl No. 21A.

now If the gta has taken registration and since his all services is either exempt or fall under Rcm. .He should cancel his registration or not

Registration and cancellation is optional.

Registration must if GTA claims ITC on their input services and he need to charge 12% on their services to both RD and URD.
As per above recipient need not to pay under RCM and he can take 12% as ITC which GTA charge.
Other wise RCM applicable for GTA service recipient.