Grossly disgruntled by online upgrade

It's more than 12 years that I have been an MTN contract customer. My nightmare started on 22 June 2024 when one of the sales consultants talked me into an upgrade. I wasn't THAT ready, but the way she insisted, I thought, let me just get the phone. I should have stuck to my intuition and do it later. My woes haven't stopped, despite " promise to pay" , trying My best paying up to a thousand per month( which I had told the consultant " I CAN'T" My salary won't allow. I have been left in arrears, sim card suspended abruptly. When I call, one consultant tells me " don't worry, your account is now up to day" after 5 days the sim card is suspended. I don't really know how to get out of this quagmire. I used to love MTN but mmm I wish they can take back the phone.