Nokia :: 5530 Switches Off During Calls / Tried Reset

Detailed log of re-occurin issue:I purchased the nokia 5530 in december 2009.In late march 2010, I added a screen protector to the phone.I also upgraded to the 2.0 firmware.Then in April 2010, phone started to switch of when making a call or answering a receiving call.After googling like crazy, removed the screen protector, reset the phone using the codes from this site. Phone worked for 2 weeks no problems.After the 2 weeks it happened again, I repeated the process and it stopped switching off. The screen protector was never replaced thinking it might be blocking the proximity sensor.In late may I updated to new firmware 3.0. Phone was functioning normal at this time.Now it's june and problem started re occuring since the 10th of june.I am unable to answer or make calls with this phone despite my many attempts using reset and factory reset , removing memory card and switching sim with a new sim card etc.So far, the only way it works is with the headset plugged in, but this is a temporary fix. Once the headset is removed during the call it switches off.Also it also crashes when making skype calls which i also installed in may. I used skype for most of may and june, with no problems.My sister also purchased the same phone at the same time, from the same vendor. She never updated the firmware and also has a screen protector installed. Her phone has no problems whats so ever.