I thought they went up for everyone? You're still paying 8? I was paying 10 for the past like 8 years and mine just went into 14 last month. I opted for the yearly plan at $140 so it's 11.66/mo so it lessened the blow. I envy you if you're still paying 8.
If I remember right, people who had YouTube premium got grandfathered in at a lower price, but that lower price didn't last forever and recently went up.
However people who signed up early for play music all access were told they would get an $8 a month price for signing up early, and that price has persisted until now through all the other price hikes and the change to YT Music.
I signed up for Google play music/YouTube red I believe in 2015 when I got my nexus 6P. It was 10 a month then and I've been grandfathered till now. When the prices went up last summer, I was told I had another 6 months or so to keep my grandfathered price before mine would go up as well. Did the OG 8 dollar users not get that email?