How to request a refund for an accidental subscription on Ultimate Guitar app?

In most cases all transactions in the App Store are final. At times Apple may provide a compassionate refund, but it should never be expected.

Some apps will have a free trial for subscriptions to let you try it out first, but you are not able to turn every subscription into a free trial by requesting a refund for it later if you do not like it. It is your choice whether you want to support an app that does not offer a free trial to allow you to try it out first.

None of us work for Apple or even speak for Apple. To contact Apple directly you can do so at this link:

Contact Apple Support - Apple Support

What happens when you try to request a refund? How is Apple not allowing you to request a refund? Do you really mean they won't allow you to do the request, or do you mean they have refused the request? If the latter then realize that Apple considers any refund to be an exception. They may allow the occasional one at their discretion, but making multiple requests for pretty much the same item may be regarded as excessive.