Telkom have no answers

We are signed up to telkom for a 50 gb WiFi bundle, this month our WiFi was recharged and we continued to use it for work and school like needed a few weeks ago our WiFi speed became so bad that we couldn't get onto Google never mind the other platforms we needed to work on our connectivity was pathetic. We phoned customer services and they advised us to reset our modem which we did however it did not improve we contacted them again and they said they would send someone out to take a look at the issue which up until this moment no one has come, for about a week this continued, at this point we had 12 gb left we decided to stay off the WiFi until the issue was resolved so we did not use it at all, until Wednesday when the connectivity improved however we went to check how much data we had left and found that we only had 3 gb left even though we weren't using the WiFi and our network is hidden and secure we contacted telkom again and their response was pathetic and rude "there is nothing we can do to help make sure you know who is using your WiFi." telkom is rude and their customer service is pathetic this is the 2nd time it has happened last month 36 GB was ****** from us on our HIDDEN SECURE NETWORK. And telkom have "no answers" never trust telkom.