Cell C is ****ming people

Good day...I had a 2 years contract with Cell C which ended in 2019 fully paid, They continued deducting when to one of their branch in waterfall Rustenburg the said i should pay a closing amount which they deducted but still continued deducting then I stopped the debit order today I was contacted by their lawyer saying I didn't cancelled the contract therefore I owe Cell c .What on earth ids this????