Your supplier, ABC Security Services is correct. Do not go by the name. You are to go by the exact nature of service being provided.Manpower recruitment or supply is not under RCM. Only Security Services have been brought under RCM vide No. 29/2018-C.T. (Rate), dated 31-12-2018 (effective from 1-1-2019 ) at serial no.14 , any registered person receiving Security services (services provided by way of supply of security personnel) in the taxable territory, from any person other than a body corporate is required to pay GST on RCM basis.
Security agency is not manpower supply. Both are entirely different. See the difference between the two.
“manpower recruitment or supply agency” means any [person] engaged in providing any service, directly or indirectly, in any manner for recruitment or supply of manpower, temporarily or otherwise, [to any other person];]
“security agency” means any [person] engaged in the business of rendering services relating to the security of any property, whether movable or immovable, or of any person, in any manner and includes the services of investigation, detection or verification, of any fact or activity, whether of a personal nature or otherwise, including the services of providing security personnel;
In Service Tax era also both the services were classified under separate Service Tax Accounting Codes.