Internet service

I have had the worst experience with dstv internet, I signed up and received my router last month. Since then my data has been dissappearing without me using it, only to find that there are four divices connected to the router even after I have changed the password. I have called customer service 3 times already but I'm not getting any help instead I got 1 dropped call and the other promised to call back after system reboot and never called back. Meanwhile I'm getting smses to say I've almost used up my data even when I'm not any where near the router. I want this service canceled cause I'm not buying data for my neighbors.