Employer not paying my salary for worked days, without appointment letter they told they hold that

Employer not paying my salary for worked days, without appointment letter they told they hold my salary for not serving notice period. There is no proper pay slip and salary credit after cut of date. I worked in GE T&D LTD HOSUR Occupational Health centre as medical officer from 20-1-2020 to 15-9-2020 through Life time wellness Pvt. Ltd. . I joined on 20th January till September they didn't give appointment letter, I didn't get my salary and pay slip on proper date. For salary they are paying after 10th of every month (pay calendar cycle from previous month 26th to 25th of next month), they paid my salary on 13th in 2 months and no proper pay slip for that.I asked appointment letter and payslip .they did not respond to me properly. So I sent my resignation to regional manager and HR. they told 1 month notice period (they didn't give appointment letter) is there, I said you are not responding to me so i am relieving from the duty. Now they are not paying my salary for 20 days worked in September month. For delayed salary employer told whether you got your salary or not. Is any rule for cut off date for salary.