Tax Charged by Supplier ( Security Services) - Goods and Services Tax - GST

Dear Sir, Security Service provider (Sole Proprietor) is registered under GST and has raised invoice by charging 18% GST. Service provided to a Pvt Ltd Company. The recipient of the service, paid the total amt including the GST amt to the service provider (Security Service provider) During audit, objection is raised that recipient of service should have paid RCM and claimed ITC. What is the way out? Is there any favourable case law available?