Hello- TurboTax incorrectly calculated our mortgage interest on our initial filing and we filed an amended return in early august. Has anyone received a refund yet?

The IRS is taking 6 months or much longer to process amended returns so all you can do is wait and check here from time to time :   https://www.irs.gov/filing/wheres-my-amended-return

As for the TT guarantees : 

Any calculation errors on the part of TurboTax are covered under the Accurate Calculation Guarantee.  TurboTax will pay any penalties and/or interest due to a calculation error but not any taxes owed.  The Guarantee does not cover any user entry errors or omissions.

See this TurboTax support FAQ for the 100% Accurate Calculation Guarantee - https://ttlc.intuit.com/questions/2566201-what-is-the-turbotax-100-accurate-calculation-guarantee

See this TurboTax support FAQ for submitting a claim - https://ttlc.intuit.com/questions/1901269-how-do-i-submit-a-claim-under-the-turbotax-100-accurate-ca...

See this TurboTax support FAQ for documents needed to submit a claim - https://ttlc.intuit.com/questions/1901060-what-documents-do-i-need-to-submit-a-claim-under-the-turbo...