Harassing me for an invoice that has been paid.

So, I payed my account in store, now I'm being harassed via sms, phone calls by 8 different people calling me. I spoke with the so called supervisor, who proceeds to do nothing about anything at all apart from telling me not to take legal action. And now I get another sms advising my account is in arrears after I made payment? 2nd time this has occurred too! I'm ready to take legal action. Lets see who calls me now.

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