I recommend contacting Apple Support by phone. They will transfer you to iTunes Store Support and you may be able to get a refund, though there are no guarantees.
Typically, is understanding when it comes to accidentally letting a free trial renew, but especially so if it’s a first-time or rare occurrence.
The phone number for Apple Support is 1.800.275.2273. They’re open from 5am-8pm Pacific Time.
For further reference, I recommend this article:
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