How do I do anything with no HR department at work

So I have been getting over 120 buck out of my paycheck every other week this year alone I have over 2000 dollars that I paid this year I have been paying this for about 2 or 3 years I'm not sure cause it's been so long my Question to u is we don't have a HR department and when u ask our managers any questions they say we don't know so how do I go about on finding out who is deducting from my paycheck because I haven't gotten anything about this no paperwork or anything on who is taking money from me all I get is my paycheck that says how much!