BAD SERVICE

I had a contact with Vodacom which was ending January 2020,i called in January I was told I was late to cancel I should have called in December, they will have to deduct for February I said to the consultant its okay, February installment was deducted, after 3 months or 5 I receive a letter that my account was in arrears, i didn't understand cause I had closed my account, I feel betrayed because I have been their client and always paid my account ,the consultant I spoke to didn't close my account now I'm being punished for their incompetence