Mtn service providers failling to do their work

Hi just took a data Sim with a ZTE router it arrived on last week Thursday but since then I'm not even able to use, it keeps on saying require login/authorization, I have since been calling mtn service providers it seems they don't know what they doing its a different story everyday, when I want to cancel the contract they drop my call, I honestly don't know what to do now, please help,BONGINKOSI Zulu