Lenovo rejected laptop warranty

Had purchased a Lenovo Laptop in Oct protected with 3 years warranty. A request was lodged with Lenovo service centre (Incident:protected) for a faulty USB Slot in Feb protected. An engineer visited the address with the Motherboard.However, it was found that USB was not working due to a missing 'usb plastic pin connector'. Its a very small plastic connector which somehow was removed (due to some manufacturing defect or otherwise).The Engineer refused to replace the part as he said that Laptop is damaged and hence does not come under warranty. I wrote to the customer care again and they replied that the laptop is not under Accidental coverage warranty.However, I believe that just because a plastic part is missed (which anyways I can't remove it willfully), how can the servicing of the entire laptop be refused? Also, the other USB ports have also stopped working due to the non-service of the complaint. The USB drives are completely fine (with the plastic pin intact).Hence, just because a plastic pin (of worth pennies) was missed, Lenovo refused warranty for parts worth thousands. I deliberately took a 3 years warranty at the time of purchase (with additional cost) in order to cover for these untoward incidents. But, I was refused the service which I deserved as a loyal customer.