I don’t know what they’ve told you in school,
But there’s one thing they usually forget to mention:
When you see N and G together (like in ‘sing’ ‘writing’ and ‘bang’)
There is actually NO true G! (Well… almost always)
Also, it’s important that you know that not every time you see the letter combination n+g you should drop the g.
Sometimes the g after the ŋ consonant is released. For example:
1.The comparative/superlative degree is added to adjectives such as long, strong and young: long+er > lɔŋgər
2. Certain suffixes added to a root word ending in ‘ng’: prolong-> proʊlɔŋ prolongate->proʊlɔŋgeɪt
3. When ‘ng’ appears in the middle of the word, in the root part of the word: England->ɪŋglənd English->ɪŋglɪnʃ single-> sɪŋgl
4. Sometimes the ‘ng’ represent the /dʒ/ consonant as in ‘range’
I know it’s difficult to remember the rules, this is why your safest bet is to mostly focus on making the ŋ in ‘-ing’ endings (there’s never g after ŋ at the end of the word) and that’s also the most common appearance of the sound (and I find it most noticeable).