Instructions not followed through by call centre. Why do I even have to phone?

I lost my phone and sim card while overseas. On 28 June I phoned customer care to have my roaming deactivated, but it turns out it was never done. Someone could have clocked up R20,000 worth of calls. I got lucky. I didn't want to cancel my sim as anyone who phoned me would not hear my voicemail which said I was overseas. Why does Cell C not allow us to control these things from the app? Why can't I switch my roaming on and off without phoning a service centre? Instead you have to go through a painful and expensive process of trying to phone in, only to find out that the customer service agent just didn't follow through. No way to know without phoning in again, somehow. *** doesn't work from overseas. I tried from my Skype number. Why can't you provide us with more control and peace of mind from the app when things like this happen? And self service pin not working.