Cancellation

I cancelled my contract with ADT at 28 Olympus Road Ennerdale Ext 1 in 2015, however it still reflects on the credit bureau under my accounts. I have called them several times since September 2018 and they confirmed that their systems reflect the cancellation in 2015 and promised to correct the credit bureau. However nothing has happened, not even feedback on the progress. Please assist in informing the credit bureau of my cancellation so it does not reflect on my profile, as this is affecting my affordability when applying for credit.