Welcome to the community.
I'd like to know if your phone is a smartphone (iphone/android). Also aside from the phone do you have laptop or tablet connected to Wi-Fi at the moment? What brand and model number of modem/router you have.
Feel free to check the existing thread about How to change Wifi Password.
I am glad to know that. Let me have a look what happened on your phone service.
Can you PM me your account details (username/customer ID or contact number associated with the account).