selenium webdriver – Every Vuser should pick different file name

Using JMeter Selenium for web based application so every Vuser should pick different file.
Ex:-” User1 —->Payroll1,User2——>Payroll2,User3——>Payroll3,User4——>Payroll4……”
So written the groovy scripting like this enter image description here
Calling the parameter in the script as this enter image description here
enter image description here

But still EverVuser is picking the same file.
Ex:” User1 —->Payroll1,User2——>Payroll1,User3——>Payroll1,User4——>Payroll1….
next iteration it is picking like
User1 —->Payroll2, User2——>Payroll2,User3——>Payroll2, User4——>Payroll2,”

Could anyone please help me