Settled account

I Settled my account with Vodacom . I went into the store . We phoned customer care . They sent me an amount to pay . I paid that amount and sent them proof . Yet I keep getting calls from VVM on behalf of Vodacom saying I need to pay 700 rand and now threatening my credit score . Why would I pay R 10000 plus and then not want to pay R 700 and after many years with Vodacom not missing a single payment and settling my account now I must be treated like a ******** ???