Retirement tax questions

Received a Letter from IRS stating that the TT calculated tax on Social Security Benefits on Line 6B was incorrect.  Therefore, instead of an expected rebate I now owe the IRS.  After checking Pub 915, and previous several years tax returns TT should have calculated the SS tax at 85% based on my total income; however TT only calculated about 26.5%.  My research agrees with the IRS letter I received. It appears to me as a TT Software calculation issue with determining SS Benefits for line 6B.  We filled married, filing jointly.  What are my options to get TT to own up to their apparent software issue and reimburse for additional taxes I have to pay because of TT calculation error.

AG