What was l charged a late filing fee when the tax date was extended?

There is not a late filing fee on a federal tax return.  Penalties and interest for failure to file and failure to pay are only assessed by the IRS and you are sent a bill in the mail by the IRS for those fees.

You are probably referring to the Penalty for Underpayment of Estimated Tax on the federal tax return, Form 1040 on Line 24.

IRS Tax Topic - https://www.irs.gov/taxtopics/tc306

If you didn't pay enough tax throughout the year, either through withholding or by making estimated tax payments, you may have to pay a penalty for underpayment of estimated tax. Generally, most taxpayers will avoid this penalty if they either owe less than $1,000 in tax after subtracting their withholding and refundable credits, or if they paid withholding and estimated tax of at least 90% of the tax for the current year or 100% of the tax shown on the return for the prior year, whichever is smaller.