Unplug the battery from the phone (handset) for 1 minute and also do the same for the base simultaneously, replug them and repair the to each other if you have to and then give it a try, also try and clean out the mic holes eat the bottom of the phone and make sure its not on must , do not disturb, or any other feature enabled that a would cause you to have such undesired function. I hope this help and for expert help you can find it here
https://www.6ya.com/mr.mike and if you need more help you can always ask another question