Tier 2 visa withdrawn by sponsor, need advice

Hi

Please help me clarifying and giving advice.

I have switched my visa tier 4 to tier 2 general in this October and according to my COS my work start from November. But my boss informed me that due to his circumstances changes , he has to withdraw sponsorship and he informed me this just 2 days after I got the visa and before my work start as per COS. I am working this office since last three year and still I am doing but in lower position . I have to start my work in new position as per COS from this November but as my sponsorship is in withdrawing process and I could not make it and I am doing same lower position job. And yesterday my boss informed me that he has withdrawn sponsorship of my tier 2 visa. And till now I didn't get any letter from my office and ukba as well. Now I don't know what to do ...and I have following question plz help me giving advice.

1.I have visa upto 2017 November but I think my visa will be curtain and I need to reapply for extension, how I can to that and how many days I will get for that and from which date.

2. Since I haven't started my work as per COS and my visa is withdrawn , is there any option for that situation.

3. I am continuing of my previous lower level work as I am still in that office,will this be problem ? and have to leave work immediately.

4 can I switch to tier 4?