MTN faulty router

Hi, I'v signed up on a fixed wifi contract with MTN. A ZTE MF286R router was included. The problem is, the router restarts itself over andover again. I phoned in, to report to he problem, and I was advised to take the device in-store. I took it to the Maponya mall, they sent me to Southgate mall. The lady at the MTN store at Southgate, told me that my device was already "booked in" (which i know nothing about), and they cannot accept the device. What should i do? I'm losing my data that I'm paying for. And if the device get's booked in eventually, will i lose the data for the duration of the device repairs?

Thank you, Eugene