In and of itself, mortgage interest and/or property taxes won't directly increase your refund. These deductions are called itemized deductions and the only reduce your taxable income. With that in mind, here are a couple things that could be happening -
Standard Deduction already applied: For 2017, the standard deduction amounts are: $6,350 (single), $12,700 (married filing jointly), or $9,350 (head of household). Every taxpayer starts off with these amounts in deductions as a "base" deduction from income that the IRS allows. So, you will need to have total itemized deductions (things like medical expenses, mortgage interest, property taxes, charitable donations) greater than these amounts before you start to see an additional tax benefit from itemizing your deductions. You are only allowed to use one - either the standard base deduction or the total of all your itemized deductions.
So, make sure you finish out your deductions, because if mortgage interest was the first deduction you entered, then you were already receiving a tax benefit from the standard deduction, so it may not have appeared to make much impact on your return.
Other Deductions and Credits: Again, deductions don't directly increase your refund themselves, they can only reduce the amount of income that you have to pay taxes on. So, it's possible that you just may not have much tax liability left for it to reduce if you have enough other deductions or credits. Credits such as the Child Tax Credit or educational credits can often reduce your tax liability immensely. If this were the case, you might not see much further benefit from itemized deductions.
