We will disprove the claim.

Consider the group where . Also we need . Using the above relations you can show that is a group. You can also show it is non-abelian by observing that .

Note that is generated by any two of .

Now show that if any subgroup contains then . If , then index of in is 2 and thus is normal in . Suppose , then one of or must belong to . But then .

We can proceed similarly for the case where a subgroup contains or .

The only remaining case is that does not contain , or . In this case , which is the center of and thus is normal in