House Owner harassment by not returning part of security deposit

We live in a residential society where 20 out of 40 flats are owned/leased by one person. These 20 flats are run commercially by accommodating 6-7 seven individuals collecting 6000-7000 per person per month with a months rent collected as a security deposit upfront. When a individual plans to leave the place, owner deducts around half the security deposit with various silly reasons. Some people would ignore considering it a small amount but some while leaving in a group it accounts for 10k which happened for one of my close associate. 5k for a person who vacated our flat very recently. Thus there are around 15 people of us who has suffered like this and there are many more. Once we have approached Police Station to file a complaint and the have resisted as the same is a small amount and that mentioning this is a Civil case. Appreciate if anyone here can direct us / guide us, that would be helpful if not to gain back whats lost but not to let this happen to many more going further. Thank you in Advance.