Tier 2 Application Delays

Hi, My application for Tier 2 was submitted in-person but was referred for further checks, After that I received a letter from home office requiring further documents which I provided in the due time-frame. Now it has been 3 weeks since they have received the required documents but I am still waiting for their response.

Also, my CoS is expiring in a month time, what are your thoughts?

Many Thanks

Only one - Wait patiently!
It may be weeks or months before you hear anything.

Your CoS has been used (when you submitted the application) .. it doesn't matter now when it is due to expire.