So you took the test in person?
Yes - you need to worry. This is serious. You need to submit proof the results are real and you took the test. Failure to respond to IRCC's email will result in a refusal and 5 year ban from Canada.
Did you apply through an agent? Any chance that agent submitted fake results? It's very unusual for IRCC to say that IELTS results are fake when they are not.