A 2018 extension request is only good for a six month extension to file a tax return until October 15, 2019. Any taxes owed on the 2018 tax return had to be paid on or before April 15, 2019.
The IRS does not have a receipt of your extension request filing. You can get a free transcript for your Record of Account which will shown the date the extension was received by the IRS. You have to complete, mail or fax a Form 4506-T to get this transcript type - http://www.irs.gov/pub/irs-pdf/f4506t.pdf
Or use this TurboTax website for any status of an e-filed extension or tax return - https://shop.turbotax.intuit.com/efile/efile_status_lookup.jsp