After you file

Sounds like you are confused.   You are saying that you paid your TurboTax fees by credit card.  ("TurboTax was paid separately via my credit card")  If you really did that, the third party bank would not be involved at all.   The third party bank----SBTPG --- only gets involved when you do NOT pay your TurboTax fees upfront using a credit or debit card and choose instead to have your fees deducted from your federal refund.   The third party bank provides that "refund processing" service for a fee of $39.99 (or $44.99 in CA)   Check your own credit/debit card statement----do you see an amount that you paid to TurboTax?

What is Refund Processing Service?

And  you are saying the IRS changed your refund from $6583 to 45 thousand dollars?!    ("Originally the amount was $6,583, but IRS is refunding about $45k. ")

If your refund was changed to that amount, it is no surprise that it went under review.   What do you believe the IRS changed that could result in a refund that increased by more than thirty-eight thousand dollars?

TurboTax gets no information at all from the IRS after you file your tax return.   TurboTax cannot contact the IRS on your behalf, so no one at TT would know why your refund changed.  The IRS will not tell anyone at TT anything at all about your refund.

Have you contacted the IRS yourself?   What does it say when you check your IRS online account?

https://www.irs.gov/payments/your-online-account

To call the IRS:IRS:  800-829-1040  hours 7 AM - 7 PM local time Mon-Fri

Listen to each menu before making the selection.

First choose your language. Press 1 for English.

Then do NOT choose the first choice re: "Refund", or it will send you to an automated phone line.

Instead, press 2 for "personal income tax".

Then press 1 for "form, tax history, or payment".  

Then press 3 "for all other questions."

Then press 2 "for all other questions."  It should then transfer you to an agent.

Your tax refund was not sent to TurboTax.   TurboTax does not handle your refund at all.

Santa Barbara Tax Products Group, LLC  (SBTPG) is the bank that handles the Refund Processing Service when you choose to have your TurboTax fees deducted from your refund. This option also has an additional charge from the bank that processes the transaction. 

You can contact them SBTPG, toll-free, at 1-877-908-7228 or go to their secure website www.sbtpg.com 

https://ttlc.intuit.com/questions/2580357-who-provides-the-refund-processing-service

https://ttlc.intuit.com/community/refunds/help/who-provides-pay-with-my-refund/00/26410