You should contact Yahoo Support on an urgent basis if you notice any abnormal behaviour with your Yahoo Account, such as your account being accessed from different locations or your credentials getting changed itself. In these circumstances, you need quick action to secure your account, and the best available option is to directly reach to yahoo mail customer service phone number who can quickly help you to change your password and recover your account and also provide you advice to ensure that you don’t face the same problems again in future.
https://www.contactyahoohelpdesk.com/yahoo-customer-service/