Hello AKhil,
Not sure if this will hel you, I implemented a similar process as you sometime ago. i hope these can be useful :
1) create Service PO with account assigmenr "U" ( unknowed)
2) HR employee : infotype 0315 assign PO item ( not cost center or activity type)
3) create CAT2 for employee and enter network activity ( the PO item should be taken by default) and hours.
4) execute CATM .. The system should generate a SES with account assigment the network activity and service price.
5) confirm SES
Not sure if I've forget something...
Regards