Suspect funny business with voucher and pin numbers.

My top up voucher had already been used, on phoning Vodacom there is nothing they can do. I was given the number that it was used to top up, but person unknown to me, cannot speak English. I wonder if someone at Vodacom who has access to the voucher and pin numbers gave my pin to someone because they noted that it was purchased on 24th July and not used by 31 July. Value of R110.