Box 2 is for the amount the school billed you for in 2016. That does not mean you actually paid it in 2016. You may have not actually paid it, until 2017. So you need to prove that you actually paid the billed amount in 2016. You can do that with receipts. You can also log into your online college account and go to the financials section of your account. Some colleges have separate columns for date you billed, date you paid, and the date your payment was credited. All three dates don't have to be in the same tax year. But if you can't show the IRS something that shows a date paid in 2016, then you didn't pay it in 2016.
Remember, qualified education expenses are deductible in the tax year you pay that expense, and it does not matter what tax year that expense may have been *for*.
You don't .... you need to prove that the school actually got paid. Get a copy of the billing/payment from the college that shows the payment to the school no matter where it came from.