bad bebt and debt collectors harrasing me

im honestly tired of writing reviews for Telkom, i went trough my finances to find that i have been blacklisted by Telkom. when i called in, i was told there everything look fine on their system and i keep getting calls from another debt colledction company saying i owe Telkom R800 and i must pay them back. i called Telkom again and they said that the money i owe them is for porting simcards to prepaid. they cut their lines months before i paid up their account and have never used the sim cards. they want forms that i filled in in 2014 showing that account is paid up, whih sim cards am i porting. this is really frustrating and irritating at the same time. my question is i have been blacklisted for some time for the R300 that i was never told about and 4 years they come back saying i owe R800.00. i was this bad debt written off lifted off my name and my name be removed from this debt collecters who keep harassing me. i call Telkom they know nothing about this 800 and when i confront these debt collectors, they say the mendate was received from Telkom.