Just a word of advice for next time you help someone, if you are going to critique them, add some helpful advice or motivation, otherwise don't bother. Okay? Thanks.
I think you're reacting far too strongly and negatively to Toritoribe-san's post. It clearly wasn't meant as a personal attack (he even cushions his statement with "I'm afraid to say this..."), but merely was pointing out that you may want to read his explanation more carefully, as well as review the fundamentals of how to use these expressions he's teaching you.
In your post above, you say "I only needed help with the letter", but please understand this is a Japanese
learning forum, so people here have a vested interest in actually teaching things in a way that will stick, rather than just offering corrections that the learner doesn't really understand.
It can be very,
very frustrating for a tutor when it seems that a student isn't taking time to fully consider the explanations given, resulting in the same questions being asked or the same mistakes being made over and over. (Think of the old "Give a man a fish..." proverb.)
I hope this doesn't come off as rude. Just trying to help you understand where one of our most knowledgeable and selfless forum members is coming from.
Anyhow, to spell out what Toritoribe-san was saying about direct objects with する verbs, either 「日本語を勉強しました」 (the noun 日本語 being the direct object of 勉強しました) or 「日本語の勉強をしました」 (the noun phrase 日本語の勉強 being the direct object of しました) is valid. The version you had (with two direct objects marked with を) is ungrammatical.