Account not closed

I took a laptop contract with Cell c in 2018. Early last year I called to get a settlement amount and I paid the settlement to get the contract closed. Now I'm trying to apply for a bond I'm told I'm in arrears with R410. Why didn't I receive any notification if that amount was still outstanding? Now I won't be able to get my kids a house because of R410 that I could have paid long time ago? When I call Cell c they say I must call Legal department but at the moment they not taking calls they only respond to emails. I've send an email no respond. I need an explanation and solution from Cell C because now I need to buy my kids a house