Below are some tips and recommendations that may help: 

1) If you have a wi-fi router/modem and/ or a wireless or cordless phone system (e.g. Digital Dec 6.0 or similar) nearby your Call Blocker, we recommend using a longer patch cord in order to allow at least 1-3 feet separation between your Call blocker and your other equipment.  This will help reducing the interference that may be caused by the other telecom equipment which may be affecting the functionality of your call blocker. Please see diagram for illustration.

2) You may also try installing the Call Blocker in parallel using a 2-way splitter (please refer to manual installation option 2),  or using another phone jack (if available) to see if this helps.

3) If you have a VoIP service with a modem e.g. Ooma TELO, you may need to use a special patch cord to reduce the amount of current going into your call blocker.  Please refer to this blog for more details:  If you would like to try this special patch cord. please contact us.

4) Also, we have received a few complaints from clients using standard voice services from providers such as AT&T, Comcast, and CenturyLink. However, this issue only affects a very small group of users within each provider, mainly users located in rural areas. We suspect that these providers may be using non-DTMF compatible equipment. Please note that 99.9% of users on AT&T, Comcast, Century Link, etc do not experience this issue.  So, if you still have this issue, then you should contact us to request an exchange.