Woonderboom junction mtb store is a ****.

So my mother purchased a rooter from mtn store on the 31st of August ans she paid 500 for the monthly service of the rooter ans 150 for the sim activation which is the rooter and to our understanding the rootet had to run for the whole month unfortunately on the 04th the rooter required us to pay another 500 for what we dont know we called woonderboom junction store which is where we made the purchase and even went there without getting any assistance instead they insist we should pay for the 500... Mind due this is the second router we took with mtn and the first one was very much fine as we stand they took their rooter but still say we owe them how can we pay 1000 for using a router for 4 - 7 days?