Bad

I was in a process of applying for finance to purchase a pre owned car,after my application was declined due to my name being blacklisted, only to find that I have a debt with DMC that was not settled about 10years ago!! I made means to contact then I was told I still haven't settled my Nashua Mobile account I took in 2008. The amount I owe is R5500... Because I knew I once took a cell phone with them I agreed to make payment. I made a payment of R500 and I've been trying to get hold of them but then doesn't even ring nor does it go through there's not even a voice prompts to leave a message. My problem at the moment is that after I've made payment now I can't get hold of them to make sure they received the payment. Also why did they not contact me as I've been living in the same address and using the same since. Now I have R5000 that I need to pay for something I could have settled before the amount becomes this high... I need help with this issue urgently please