I have a credit card in which my limit was 2k however, my balance has jumped to $2800 due to late fees. According to my credit report it is noted as a "charge off" and a collection agency calls me three times a day regarding my account. What should I do?
If I don't pay it what will they do?

It will get ugly, especially if you are gainfully employed or have any attachable assets. If you have any cash you can pay in a lump sum, your best bet is to ask for a settlement & be done with it. If not, you need to ask for a repayment agreement that you will realistically be able to pay. It is not a good idea to ignore them.