Router problem

I bought a Huawei B315 router from Telkom Mall of Africa Store earlier this year and it was working fine. Starting from 2 months back data is depleted the same days just hours after.

I took the router back to Telkom Mall of Africa store and a technician gave me some trouble shooting steps and we changed the password.I then bought another bundle and when i got home i monitored the consumption and it depleted it with no device connected,i am talkinh 20gb.

So Today i brought it back to be checked and the store assistant told me that they will charge me for booking it in for it to be looked at by the technical department. I mean the warranty is valid so why should I pay.

I feel let down by Telkom Mall of Africa,the responsibility to ensure that the device is working rests on you as the supplier and service provider and I expert you to give real assistance when your product is not working.I have not been helped at all and maybe forced to cancel the contract.