Parthetic service

Where do i even begin with their pathetic service from call centre where they all say different thing for 1 issue or mute you if you raise concerns with them or when you finally send email each day different consultant would respond asking for your personal details tjoooo i am so so ****ed , such a big service provider with this kinder of service, all i needed was a replacement of fixed LTE device for my wi-fi which did not last even 3 months on receipt but they have dragged the matter the whole month still have no resolution watsoever yet i have paid for their services n***x