I have two job offers in hand, one that I initially accepted and my references has been sent already

I have two job offers in hand, one that I initially accepted and my references has been sent already. But it’s been a month since I heard from them last. Tried mailing as well as calling them, all in vain. They haven’t confirmed yet whether my references have been accepted or not neither they wanted my details to apply for the CoS and to be honest this absolute silence is getting really frustrating everyday. And I know people who are waiting for 3 months for CoS from the same trust.

Considering that I have another job offer in hand and I haven’t yet got any confirmation regarding COS 1.5 months after accepting the job formally, would there be any problem to accept the other job and decline the first one? Will there be any consequences for this kind of action? Please guide me through your kind suggestion.