could NDS possibly get any worse?

My cellc contract has been cancelled about 4 months ago and a final manual payment had to be made as the last debit order doesn't go through, it has to be manually paid, as was done, 4 MONTHS AGO!!! NDS keeps phoning me at odd times of the day and night telling me to pay my account and refusing to reconcile their records with Cellc. This is beginning to feel like harassment and I'm becoming highly irritated. Could someone in this company please wake up and do their job!!! :( :( :( my number is *** if this will not fall on deaf ears.