Dell India — cheating by workers of service center

Sir, i have a complain against the service center of dell which is situated on chittranjan avenue, trust building, block a, kolkata.
I submitted there because my screen is not working properly they told me that you will pay for it because your screen is damag but i received 3 messages and 3 calls by the dell company that your issue is resolved please vist service center and collect it but when i vist there i found my laptop is in same condition. And when i ask them taht a got a mail and phone call they are lying that i don't know about call if you want your laptop proper conditon then submit 8000 rupees.
What's this. Company told me that your laptop is in warranty and another side center workers taking the money.
They return my laptop in my same condition and told me that submit 8000 then i will repair it. Please tell me how i will complains against them.