Individual circumstances vary. If you believe MTD does not apply to you, check your qualifying income and circumstances against the official GOV.UK guidance first.
Common reasons HMRC's letter might not match your own view include: income that is not qualifying income, a recent change in your circumstances, or income that falls in a different tax year.
If, after checking the guidance, you still believe HMRC has contacted you in error, contact HMRC directly. Keep a note of the date, the reference on the letter or email, and what you discuss.
MTD Together cannot resolve disputes with HMRC or tell you definitively whether HMRC's view is correct. For that, you need HMRC or a suitably qualified professional.