What mistake was made? You do not have to pay to post questions here in the user forum.
Phone support is not provided with the Free Edition. If you are using a paid version of the software or if you purchased PLUS you can get phone support when customer support is there. Otherwise, post your question here and someone will try to help.
To call TurboTax customer support
They are available from 5 a.m. to 5 p.m. Pacific time Monday-Friday
What is the mistake you think was made on your tax return? Did you receive a notice from the IRS concerning your tax return? If so, what is the notice number that is located in the upper right corner of the first page, usually preceded by either a CP or LTR.
The Free online editions are only for very simple tax returns so there is no Live TurboTax phone support. You can ask your question or describe your problem here at no charge and someone should be able to help you.
See this TurboTax support FAQ on how to contact Support - https://ttlc.intuit.com/questions/3401489