Is gst on transportation charges?

Yes They are absolutely correct , (Refer section 8, & 15 CGST Act)

Yes they are doing right

Since the case above is a type of Composite supply i.e where goods and services provided together which is owing to natural necessity.
Nd we too can find principal supply being here is Icecream🤤, hence GST applicable on the 11000 shall be as per the 18%.
moreover, I liked the clear cut details mentioned by Vishesh Surana

WE ARE GTA TRANSPORT CONTRACTOR, WE SUPPLY THE TRUCKS TO BIG CORPORATES ONLY LIKE GODREJ,HINDUSTAN LEVER, BRITANIA INDUSTRIES, ETC., FOR EXAMPLE CORPORATE ASK ONE TRUCK FROM CHENNAI TO MUMBAI WE CHARGED FREIGHT RS.20000/= AS PER CONTRACT  HOW TO SHOW THIS GSTR1 BEACAUSE WE ARE REGISTERED CONTRACTOR AND SUPPLIED TO REGISTERED PERSONS.  AS PER CGST RULE SEC. 9  GTA IS EXEMPT. BUT CORPORATES WILL PAY 5% UNDER RCM.  HOW TO SHOW THIS IN GSTR1 KINDLY EXPLAIN

SHOW IT UNDER TABLE B2B, BY CLICKING OPTION "RCM"

thank you and congratulations