Paid Up account letter - still getting calls and still in Default Months later??

Aai, so tired of dealing with this company! Paid my outstanding amount up fully in July, received a paid up letter from cell C on 29th July, and was told my "In Default" on my credit report would be gone in 21 days. 2 months later as at end September, guess what? the "In Default" is still reflecting on my credit report, preventing me from fixing anything in my life!

And I am getting agencies phoning me about this still!!!