I do calf raises every Friday, it's the only exercise I do for the calves.
from Saturday to Monday I find it really hard to walk as my calves are in extreme agony, it calms down on Tuesday and back to normal for the next 2 days. I've even lowered the weight, reps and sets I do but it's still the same (I can easily lift the full 200kg stack for 4 sets of 20 but I don't anymore, I'm now nearer 100Kg for 2 sets of 12).

Any ideas what I can do either instead of calf raises or to stop it hurting so much (I stretch and warm up with light weights)

Try doing it more often than one a week if the pain is just DOMS. ie 3 times a week. Or leave it out and let it get worked during deadlifts/squats
Or maybe stop stretching and see what your calves are like without it.

it doesn't feel like DOMS, it feels a million times worse, there's no way I could do it more than once a week, I really struggle to just straighten my legs because of my calves. They don't really feel like they are getting worked during squats, but I think I'm gonna have to just avoid doing them from now on as it's getting unbearable (I've tried without stretchin, no different)

If you can handle the extra weight, i would do that but just 1 set to failure should be all you need.

Tell us your exact training routine for calves.

Spend alot of time stretching them between sets, and for another 10 minutes after your calf workout.

Tell us your exact training routine for calves.my exact calf routine is calf raises, that's it (as stated in original post)