Bad service

I'm trying sins beginning of this year to cancel my phone contract that endit I gave notice they took the last payment then 3 months after that vvm attorney contacted me for money I gave them my banking statement showing cell C took money and the email were I canceled they stop calling me now cell C starts again if I send mail to there Collections department they just send you a mail that they received your mail back and they don't contact you my account went from R306 to R700 that they now demanding