Vodacom arrears for a cancelled contract

i had a contract router with Vodacom, which has never worked even a single day because of network issues , i reported the problem and they took 3 weeks to get back to me ,eventually i cancelled their contract and it took them another month to collect their non working router, i did about 2 reversals after they collected their router because they kept on debiting me for their incompetency , wrote to hello peter and the issue was sorted and they cancelled the contract, now i am getting calls that i owe them R135,63 and if i do not pay them they will hand me over , every time i asked what is that money , i not getting any answers , it is just arrears but not an explanation on what is it for exactly.

can someone that actually knows what is going on call me.