Stop cycling…I’m not sure why anybody would train if they are constantly in pain you are just making it worse (I’m not sure why anybody does 100miles on a trainer either but that’s a different story). If you can’t walk you have done some serious damage (I often have been unable to run from injury but rarely unable to cycle) You need to ice it, rest, get to a physio specialising in soft tissue work and get it assessed. If it was a mild strain you could get away with rest, stretching and foam rolling but it sounds like you have a serious injury. One point you could check is that sometimes hamstring pain is referred down the leg by active trigger points in the glute medius and minimus or compression of the sciatic nerve due to a tight pyriformis. You can address trigger points with a lacrosse ball…however it looks like a good old fashioned muscle tear - which will need lots of rest. Hamstrings are really tricky to heal and have ended the career of many an elite sportsman - take it very carefully - this will not go away and you can’t train through it…which looks like what you have been trying to do!