Is 去 (qù) pronunced /tɕʰu/ or /tɕʰy/?
I think it is a terrible mistake that the website has made, because there is no occasion when qu is pronounced tsʰu in Mandarin. Since you can actually tell the difference between u and ü, things should be easier for you now. You can just memorise that after (pinyin) j, q, x, y, ü is always written as u, and if you see u after j, q, x, y, it's always pronounced as ü. It shouldn't cause any confusion at least to native speakers because these consonants are never followed by a vowel sound u but only by a ü.