Bad service by MTN

Bought a Huawei p smart 2021 on a 36 month contract from MTN via Mondo. The phone got delivered and a month later after my 1st debit. The data stopped working while i had a full 4G network active. MTN told me they're seeing network barring and they'll remove it. Same problem kept occurring and now it cut off my WIFI connection to everything. Bluetooth also stopped working for two weeks now. Been on the phone with MTN to sort out the issue. I'm told that if bought online then Mondo must deal with it. I called MTN again for cancelation but I'm not getting through to the department. I wont pay R300 for the next 36 month for a device that malfunctioned on its second month. I need the device replaced or no payments will be made. this is clearly a demo device that was delivered. MTN told me to stop by their stores to check for the warranty of the device. I NEED A NEW DEVICE. 36 MONTHS IS A LIFETIME i honored my contract by paying. But not for a demo device, do something about this Mondo and MTN.