Apple refund request denied for Meitu subscription

My free trials for subscriptions are something I always always always make sure that I cancel, and I know that I cancel them. But one app, Meitu, ends up charging me the full price of the subscription even after the trial ends or if I’d cancelled it early - I don’t understand why this happens when it’s not listed anywhere that this is the case. It says that I can cancel anytime, as it does with other apps. I’ve requested a refund from Apple for about $60(?) before but it was denied for not being valid or some sort of explanation like that. It’s happened again, except this time I’ve only just placed the refund request and I’m worried it won’t work again. How do I make sure that my refund request is accepted? It’s a lot of money, this time it was about $70. I don’t want to be someone that complains but I really really want my money back - is it an Apple problem that should be taken up with them or should I contact the app support? :(

[Re-Titled by Moderator]

Original Title: Refunds not accepted