When I try dialing in to my service (and to save time I'm sure I'm dialing the right number) I hear a dial tone and a handshake but in the middle of the hand shake it goes into a deep beeping ringtone and won't stop till an error 678 message comes on. Now if I try another number, the same but if I keep trying the numbers over and over again sooner or later I get my connection, how to fix this problem, thank you.