Would some body tell me how to face this situation without being any problem.
Yes. Dispute the fraudulent charges and cancel the card. As far as dealing with them, the less communication you have with blackmailers, the better. Ideally, anybody in your situation should just delete their first email without even responding and block their email address. If you already made the mistake of responding, just stop responding immediately, delete their subsequent emails, and block their email address. For them, it's like fishing: the first demand is their version of dropping the lure into the water; if nothing bites the lure, they'll just pull it out and drop it back in, looking for fish somewhere else; if you bite, they'll continue trying to pull you in; but if the line suddenly goes slack, they'll just re-bait the hook and drop it in again, looking for fish (meaning other victims) in a slightly different spot. They don't really have anything to gain by contacting your school, because they lose any leverage once they kill the hostage; and if they do, it only increases the possible risk to them, because you'll publicize your experience and make it searchable by their company name on forums such as this one. So, regardless of how much contact you've already had with them and/or how many mistakes you've already made responding to them, just let the line go slack ASAP by not responding again, at all. Proceed with the credit card dispute of the fraudulent transactions on a totally separate track without any direct communication with them.
However,
your unique situation is slightly different because of one new element that I don't think anybody else here has ever described doing: If I'm reading your post accurately, you also disputed the original (authorized) transaction. That wasn't a good idea; because you've now put yourself in a situation where they actually have much more incentive to retaliate. If you never submitted their project, I guess you could ignore them and take my general advice, above. However, (especially) if you did submit their project, you should immediately cancel your dispute of the charge that was originally authorized, so that they don't have that extra incentive to retaliate for that. Send them one last email apologizing for accidentally disputing the original authorized charge and informing them that you'll be cancelling (only) that part of your dispute, and
then, follow all the rest of my advice above and don't respond further to anything more from them. Block their email address so that you don't even see their subsequent messages and ransom demands.