warranty is not provided on my lenovo phone by service centre

i bought a lenovo phone from flipkart around 4 months ago. last week i faced some problem in touchpad and i went to service center at shakar pur service center and reported my problem. they took my phone to check and few minutes later one guy came out and told me that my phone could not be treated under warranty as its seal is open . i was shocked as i have never ever opened that phone and also never get it repaired from any where else. i asked them sir why would i do so since my phone is under warranty i would only go to service center.seal they are talking about is juat a small paper sticker