Dear Asreet,
Yes, it has got legal consequences, if employer wants to drag it to create hindrances. The offer acceptance means you give your consent as the matter offered and is not ethical.
You should sent a mail to the ICICI bank, stating your denial to join owing to personnel problem. It is not clear from your post, why do you accept the offer and now denying.
Its an offer only it up to you whether you have to join or not. If you are not joining them, its not illegal, but definitely not ethical. Therefore, you are requested to maintain decency in your action for the future course.