HUAWEI Y635 unlock phone code

Greetings!!! I am VERY new to this type of activity (78 yrs old!!), but I am trying to find out how to unlock my HUAWEI Y635-L02 phone as I have changed my provider. Both my previous & present provider say they have changed over but my phone remains "locked". I believe that some sort of code is necessary but it is proving difficult to find someone with the answer!!
Hope that someone here can point me in the right direction.
Thanks,,, :confused: