First, tell Open English to stop marketing and delete your number. You can also take back any permissions you gave them and ask to be put to their internal do-not-call list through their privacy contacts or contact page. Write down the date of your request.
If you live in the U.S., put your phone number on the National Do Not Call Registry and say that you no longer agree to be called under the TCPA. Businesses have to respect revocations that are made in a reasonable way.
You have the right under GDPR to say no to direct marketing and ask that your data not be used for that reason if you live in the EU or UK. You have the right to this, and you might use it.
If the problem remains unresolved, consider filing a complaint on Xolvie to raise awareness about the issue and inform others.
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I Face Continuous Harassing Calls From Open English After Only Downloading App

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