Hi gülnihal128,
welcome to the Apple (user-to-user) Community.
Re: "I got scammed by Better.me app" ... "This is a scam and I am complaining"
We are all Apple users, like yourself, in the community. We have no access to your account or details.
We'd like to help, however.
A free trial of an app needs to be cancelled at least 24 hours before it expires,
if you do not want to be charged for an ongoing subscription.
To report a concern about an app, you must provide the URL of the app.
Find the URL for an app in the App Store to report a concern - Apple Support
How to report a problem
https://reportaproblem.apple.com/?s=6
or
App Store Support website (info. / support / contact options etc.)
App Store - Official Apple Support
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You may need to ensure the subscription is cancelled, so no further charges are made:
You may be able to cancel in the app itself, or on an associated website, or check for an email received:
or
See Apple Support's article: If the subscription that you want to cancel is not listed – Apple Support (AU)
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Re: "I asked for a refund, but there was neither a refund nor an answer."
The best source of help for a product not made by Apple (a third-party product)
is the company or person who made it—its vendor or developer:
How to: Contact a third-party vendor - Apple Support
or
How to contact an app developer - Apple Support
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Re: "Have any of you had an experience like this?"
We have no way of knowing what is reported to Apple, or how many, if any, may be affected.
Unless anyone answers, sharing a similar experience, there is no other way to check.
All the best :-)