If you upgraded your iPhone recently, there is a chance this option was automatically activated. Go to Settings, and in case the option is turned on, deactivated it.
As mentioned, upgrading your device can change some options, such as turning volume ringers off, for example. What you need to do is navigate to Settings, General, Accessibility, and switch on Assistive touch.
In order to clean the charging port, you can use a toothbrush, dry and clean. When it comes to 5 ways to fix iPhone 4 not ringing we provided, this one sounds ridiculous to many, but it often solves the bug, so make sure to give it a shot.
At the top of your iPhone, there is a sleep/wake button. Press and hold the button, and slide to power off. Press the same button to turn the device back on.
If the previous solutions did not fix the issue, try this one. Before you begin, backup your files. Go to Settings, General, Reset and choose the option to Reset all Settings. When it’s done, you will have to set up your device as new, which is a very simple and easy thing to do.