In my flat, I find many and many small cockroaches which makes our life miserabl

We had similar problem.. not any more!!  We use to leave unwashed plates/utensils in the sink overnight.  Also, the garbage bins were cleared only in the mornings.  Just by clearing the garbage in the night after dinner and cleaning the dishes and kitchen before going to bed, we got rid of these dreadful pests.

Depending on the severity, intially you can do a pesticide to get rid of them.  However, they will come back, if proper sanitation advise as below are not followed.

Sanitation is key to reducing cockroach infestations. Cockroaches need water and food to live and you can minimize an existing infestation when improving sanitation.

• Do not leave food out – utilize insect- proof containers and store food in a refrigerator.
• Do not leave pet food and water out overnight.
• Wash dishes when meals are over
• Wash all counter tops , sinks and tables with soapy water.
• Sweep or vacuum all cracks and crevices to remove all food and debris.
• Take garbage out daily. Always use closed plastic containers or bags.
• Repair any leaky water pipes or faucets.
• Recycle cans and bottles on a regular basis; wash and clean containers that hold recycling items.
• Increase ventilation where condensation is a problem.
• Wash garbage cans, and areas where kept. Keep Dry.

Hope this helps.

LM