If your results were not certified, you may be able to retake the test within 21 days of your original purchase, depending on your testing history on that credit. If 21 days have passed by the time you receive your invalid result, or you have less than 7 days remaining to retake the test, you may receive a 7 day credit extension. This also depends on your testing history on the credit.
However, please review and keep in mind the reason(s) why your results were not certified before retaking the test.
If you received an email saying your account was blocked, you will not be able to retake the test. If you feel this was done incorrectly, you may submit an appeal.