I re-read your posts an I think I understand what you are asking. You need $2800 to pay fees. Discover has extended you $1500 in credit. You need to find a source of funds for an additional $1300.
So long as you the full $1500 available to charge to your discover account, and it is a few months old, someone should be willing to give you another card at some point.
However, if you have a student visa and are leaving the country indefinitely in December, and need the money for that purpose. it is not likely that they will do so with graduation only two months away. It poses a very high risk to the lender.
If Capital One said no twice, and Discover has denied a request to increase your limit, this may be part of their reasoning process for denying you.
6/15 DC BK7, starting EQ FICO score 563
2/16 FICO EQ 661. TU 653, EX 660
Current CC Accounts: Capital One QS1 500; Overstock 1300; Care Credit 5000; Barclay Rewards MC 1300; JCPenney 3500; Amazon 3500; WalMart 3500; Target 500; PenFed Promise Visa 2000; PenFed CLOC 500; NFCU Flagship 12500; NFCU Platinum 8500; Credit One 1000.