I have a router with FXO card. One of the ports has a Vonage line attached to it and the other is to PSTN line. I call the vonage number and get a dial tone from the PSTN line and I then dial a local number. However lately when I dial the local number, the router randomly duplicates one of the digits of the local number. For example if I dial 937758, the router will send 9377558 duplicating the 5 digit. Can anyone please help exlain what is going on.