I'm using KT 1Gbps internet, but it keeps dropping to 100Mbps

I was wondering why my Steam game download speeds were suddenly so slow
and it turns out I've been downloading at 100Mbps the whole time;;
‌I tried resetting the router and kept testing, but it's the same result
I'm going to call them first thing tomorrow afternoon
Has anyone else using KT experienced this???
I don't know if they're throwing a tantrum because the baseball team lost or what
If this happens again, I'll have to consider switching providers