Did you choose to have your TurboTax fees paid out of your Federal refund? i.e, did you use the refund processing service? If so, that can decrease the amount of your refund. Also remember that the refund processing service has an additional 34.99 service fee in addition to your TurboTax product fees (39.99 in California, where it is bundled with "Premium Service.")
If the IRS decreased your Federal refund, you should get a postal letter from them in 2-3 weeks or so explaining why your Federal refund is less than what you filed. The letter should also tell you steps you can take if you disagree with their decision, including a contact number for you to phone them if desired. The following help article will tell you a bit more about possible causes, how to check for any offsets, etc.
https://ttlc.intuit.com/questions/1894477-why-did-my-federal-tax-refund-decrease-after-i-filed
The IRS has said:
"Examples that could decrease your refund include math errors, mistakes, delinquent federal taxes, state taxes, child support, student loans, or other delinquent federal nontax obligations, or if the earned income tax credit (EITC) portion of your refund is withheld pending further review."
https://www.irs.gov/Help-&-Resources/Tools-&-FAQs/FAQs-for-Individuals/Frequently-Asked-Tax-Question...
IRS: 800-829-1040 hours 7 AM - 7 PM local time Mon-Fri
If an offset is involved, here's more info on the Treasury's offset program:
https://ttlc.intuit.com/questions/2539782-what-is-a-refund-offset
Treasury Offset Program phone: 800-304-3107
Offset Call Center hours are 7:00 a.m. until 6:00 p.m. (Central Time).
