Disloyal provider MTN

I have been a loyal customer for over 10 years, I pay substantial amount, last 6months I was moved to cash payer, every month I paid more than contract premium, but every month got disconnected due to arrears, only to find out that debit order payer is arrears and cash is advance payer, that is why in arrears, for all these years of loyalty you guys decline my upgrade, I'm sickened at this, this is how loyal customers are treated by mtn.