I believe your problem lies with your base connection to the AX520 phone in jack.

Using the standard RJ-11 cable that came with the AX520 to connect your base unit to the Phone In jack on the AX520 will not work due to the difference in the wiring standard between the RJ-11 and BT Standard.

You need to purchase a BT socket to RJ-11 adaptor, these are very in-expensive and can be purchased from any electronics retailer.

Give iot a go and let me know if it resolves the problem.

Also you can download the latest installation instructions using the link below.

2 line Intelligent PSTN / VoIP Line Switch : Cooltronics, Cool Gadgets For Cool People