Here are some tips to help you resolve this issue.  We suggest you try these one at a time, starting with 1:

1) Make sure feature SET 6 (see section 6 in the 
manual) is turned OFF.

2) Try installing it in parallel using another phone jack or a splitter (refer to the manual for installation details)

3) Review the BLACKLIST to make sure there are no 1 or 2 digits numbers stored (refer to section 8.2 in the manual). 

4) Reset the BLACKLIST memory by removing all the numbers (refer to section 10.2 in the manual).  

5) If none of the above works, please follow the instructions on our warranty page to contact us and request a warranty repair or replacement.