Account paid up lawyers still phoning me

: Good day I had a woolwoths account witch I paid up in 2012.I paid over R7700.00 to close the account at WW Soutdale. I now receive phone calls that my account is outstanding with more than R9000.00 from lawyers. I will not pay anything else as I did close this account. How is this query going to be resolved as the store where I paid it is closed down and I don't have the proof of payment any longer. Please treat this as urgent as I need to finalise this or I will get legal action and refer this