Account query and no assistance!!

Im am getting so frustrated with MTN I’ve been a long standing client of 9 years and never missed a payment all of a sudden my account is in arrears I’ve made over 5 phone calls to mtn querying this as I have proof of payment going back to 2017 every month and every time I phone they tell me a consult will call me back this never happy and every month they cutting my phone! I’m at my wits end as no one is sorting out my problem!!!