Hello Shaylene224,
We understand that your volume is changing without you making this adjustment. First, let's verify your settings. When Change with Buttons is enabled, your volume can only be adjusted with the buttons, on your iPhone.
"Lock the ringer and alert volumes in Settings
- Go to Settings
. - Tap Sounds & Haptics (on supported models) or Sounds (on other iPhone models).
- verify Change with Buttons settings."
More details here: Adjust the volume on iPhone
Also, have you tried restarting your device to see if that helps. This simple step refreshes your iPhone and the software:
"How to restart your iPhone X, 11, 12, 13, or later
- Press and hold either volume button and the side button until the power-off slider appears.

2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo."
Thanks for posting in Apple Support Communities.
We hope this helps.