I wanted to ask is it ok to use subheadings in a letter to discuss a statement you disagree with? I ask because I just did an english language exam and the subheadings were named with the topic I was writing about. Is it ok if I used subheadings?

I think that would be fine! If you have a look at the mark scheme on the exam you refer to then that should give you more detail although subheadings are a language structure feature

I think that would be fine! If you have a look at the mark scheme on the exam you refer to then that should give you more detail although subheadings are a language structure feature