If someone blocked you on Instagram and you want to block this person too, you can not. This is how Instagram works.
There are some scenarios where this is desirable, but the Facebook photo platform does not allow this to be done, and this does not seem to have been done by accident, but rather by meticulous planning.
But in which situations would you want to block someone who blocked you? A typical situation is when you end a loving relationship with “John Doe” and he blocks you. So, John Doe now has full control over when he can see your profile. For him to see your photos, he need just to unblock you briefly, see what he wants, and then block again. Your only way to stop John from seeing your profile is to make the profile private to everyone – which is not a good choice if you are a famous profile and need to keep it public.
Many will argue that if your profile is public, John Doe can simply create a new account and look at your photos from it. Against this argument, I say that in many cases the simple “peace of mind” is enough. Not seeing John among the people who watched your Stories or videos, or liked your photos, is enough to make a traumatic end of relationship easier to face. And to know that “you did something” to prevent John from watching your life is already valid.
Instagram should review this policy and allow profiles to be blocked on both sides. This would be an important privacy and security tool.