tier-2 extension application

[shukhen001]

Hi, my Tier-2 general visa is expiring on 20 January 2016. Now I am trying to extend my visa. Can anyone suggest with the following questions:

1. Do I need a new CoS from SMS I tried "Request additional CoS or CAS" as I just need to extend my existing visa, I was refused for additional CoS. The email said to provide details for the person I need the CoS for. I am under the impression to extend my tier-2 I need to have another CoS to use it to create my new certificate. Or else do I just create a new certificate from the excising one? is there anything I need from home office before I can submit my own VISA extension application, apart from creating a CoS on the SMS..

2. My previous SOC was "2132 IT, software professionals" which is no longer available. and my salary has not increased (which is 2200). Am I safe to use 2137 which do match with the job role. Is there any negative impact on getting the VIsa as the job salary has not increased. shall I ask my employer for a salary increase!!
3. also I had visa from jan-2013 to jan-2016 which is 3 years now to qualify for ILR 5 years shall I need to put job date for 2 years jan-2016 to jan-2018 or am I allowed to use any date as long as it covers 2 years?

Many thanks in advanced for your help