Can't upgrade my contract

I have never in my life had worse service from any service provider in my life. Even telkom beats their sorry excuses. I am due for a upgrade for a contract I have had for 4 years now. This will be the second upgrade and Im currently paying R1200 pm for my contract. Im looking at upgrading to the new galaxy s21 and get told sorry sir you can only upgrade for R400 pm which is ridiculous. Ive spoken to every department they have and all just say we will get back to you which doesn't happen. Im fed up with them.I even get a cellphone allowance off R800 but sorry that doesn't count. Worst service provider ever and they still want my business?