I need a refund on a subscription

Fisrtly you should cancel the subscription please see See or cancel your subscriptions - Apple Support

Strictly speaking all purchases are final (after all, you can't very well return them): please see this page for information on requesting a refund: Request a refund for apps or content that you bought from Apple - Apple Support - note that just deleting an app doesn't cancel the subscription.

However Apple have been known to be sympathetic in cases of actual error, so it's possible that they may allow you a refund as a one-off concession: but please be aware that they are under no obligation to do so: go to https://reportaproblem.apple.com/?s=6

The subscription starts automatically after the end of a trial period: you have to cancel it yourself prior to that. If Apple have decided not to give you a refund that is their decision, and I'm afraid there's not really anything you can do about it. You could try contact Support again and try to escalate it to a higher decision level, but I wouldn't hold out much hope. Choose your country or region - Official Apple Support

In the meantime make sure to cancel th subscription to prevent further charges.

I didn’t authorize the renewal of an app subscription after the trial was over but I was still charged, I have tried to get a refund but I keep seeing this