If you are not seeing improvement with what you are doing you are not hitting the correct tissue.
It is time to re evaluate the situation.
Have you looked up/down stream of where you are seeing the issue?
Some high ham episodes
High Hamstring Gnar, Trigger Points, and Up Stream/Down Stream
Episode 354: Make Your Own Super Floss/High Hamstring & Hip Gnar Gnar
Episode 265: 100 Episodes Left, Now Go Open Your Hips
Episode 137: Best Hip Extensor (High Hammy) Mob and Better Jerk Shoulders
Episode 104: Hammer Your High Hammy
Episode 58: Weird Hamstring Problems and Simple Neurodynmaics