WiFi speed issue

In December I had a WiFi line installed a speed of 30 up 30 down. The service on installation was amazing. Now it's been 3 weeks when living streaming everything we watch is buffering. I logged a call and last week Thursday a technician came out. He saw exactly what we experiencing, he got an agent to call me while he was here so we could explain to them what's happening. The agent said he would look into it and call me back. I never got a call back rather a sms with details to login into the WiFi, I supposed he reset the WiFi. I am still having the same problem, it's got so bad that the SABC app that is on the TV we can't watch cause it's buffering.

We have 4 devices link to the WiFi 3 cellphone and a TV. Last night we tried something different to see if there would be a difference. We only had my sons phone on the WiFi he played an online game and still he had a problem.

So I would like to understand what is the issue, am I getting a call back from the support guy 5 days later to explain why he reset the WiFi and sms a new login details, why are we buffering when for 5 months we never had an issue. I am paying for a service that is not working like it should.