Paid up letter

I got a call from vvm that should I settle my RCS account before the 31st of August I will be given a 50% discount, and so I agreed. I was given the details to deposit the many, I deposited the money on the 28th of August. By the 7th of September I got a call that I should give them my email address so that they can send me a paid up letter so that I can take it to the nearest Spitz store to cancel the account, and I did. I never got the email, instead I got another call telling me I still owe the account, so when explain that I had paid they told me I should forward the proof, I asked for details but I never received them. Till today they still call once a week and ask for payment, my patience is really running thin. Thank you.