I have an older version of Microsoft software Excel, Word, etc, If I need to use into I have to pay for something I already own? How can I use my software now?

If your older version of Office is 2011 or older it is 32 bit and will not run on Catalina. If this is your situation you will need to upgrade to a newer version of Microsoft Office.

Microsoft Office

Look into the Free LibreOffice, it handles MS Office files…

https://www.libreoffice.org/

Apple macOS (Mac OS X)

The software and hardware prerequisites for installing on a Apple macOS computer are as follows:

• LibreOffice 6.3.x: macOS 10.10 (Yosemite) or higher
• LibreOffice 6.2.x: macOS 10.9 (Mavericks) or higher
• Intel processor
• 512 MB RAM
• Up to 800 MB available hard disk space
• 1024x768 graphic device with 256 colors (higher resolution recommended)

It is a recommended best practice to back-up your system and data before you remove or install software.

Notes:

• For certain features of the software - but not most - Java is required. Java is notably required for Base.
• Due to an issue, there are the following restrictions with Java: on macOS 10.10 and newer, JRE isn't found, JDK is required
• LibreOffice 4.3 can still run on OS X 10.6+, but please understand that this support ended when 4.3 was retired on May 27, 2015.

https://www.libreoffice.org/get-help/system-requirements/#Apple

Feature Comparison of LibreOffice v6.4 with Office 365/Office 2019 for Mac

https://wiki.documentfoundation.org/Feature_Comparison:_LibreOffice_-_Microsoft_Office