Being used

Am currently working as store manager yet technically I have supervisor certificate before we open new store I was appointed as new manager for the that was gonna open last year of last year 10:11.16 until today am the lowest person paid no contract it papers that were issued to me that shows my new rating how it will be I dnt know what should be my minimum or maximum of my salary should be...I once complained and my seniors asked me for the proof of appointment yet every in the company they dnt have proof we are just promoted to do more work with no relevant salary...we do same work same s**** but money is different.