[Resolved] Dead air calling out, or upon being put on hold

For the last couple of months, I've had trouble with, (I thought) just calls placed to Amazon, with the phone ringing and then hearing nothing but dead air. It was only happening with calls to Amazon, maybe about 40% of them.
As well, after being put on hold, the hold music is suddenly being replaced with dead air, and eventually the call disconnects.
Today I called a friend; the phone rang, then I got dead air. I called my friend again and got them; they said that the phone had rung and when they picked up there was nothing but dead air.
I have noticed that nearly 40% of the time, when I dial a number, regardless of what it is, that it won't even ring. I have to hang up and try again, and usually it goes fine the second try (except with Amazon where I only get through on the 5th try).
I have had to call Amazon several times today. Sometimes I get dead air after dialing. Sometimes after it rings, I get dead air. But most commonly I'm put on hold after speaking to an agent, and after a little while the hold music is replaced with dead air. This goes on for several minutes until the call disconnects. I assume at the other end someone has picked up and gotten dead air, so they hang up.
So it's maybe nearly four months that the dead-air-after-dialing issue has been going on, and about two months that the dead-air-while-on-hold has been going on. It wasn't until my friend shared their experience with my calling them that I realised it's happening on both ends.
Come to think of it, the being disconnected while on hold business might have been going on for nearly a year or more.
I wondered if it was the 15-minute problem I'd heard about, but the time that dead air sets in seems to be random.
It also seems like I'm making/getting more garbled calls, too.
This is possibly (probably?) an ATA problem (Cisco SPA122) but I haven't changed anything in the settings for a long time. I need help in figuring this out. Does anyone know what's going on?
As well, after being put on hold, the hold music is suddenly being replaced with dead air, and eventually the call disconnects.
Today I called a friend; the phone rang, then I got dead air. I called my friend again and got them; they said that the phone had rung and when they picked up there was nothing but dead air.
I have noticed that nearly 40% of the time, when I dial a number, regardless of what it is, that it won't even ring. I have to hang up and try again, and usually it goes fine the second try (except with Amazon where I only get through on the 5th try).
I have had to call Amazon several times today. Sometimes I get dead air after dialing. Sometimes after it rings, I get dead air. But most commonly I'm put on hold after speaking to an agent, and after a little while the hold music is replaced with dead air. This goes on for several minutes until the call disconnects. I assume at the other end someone has picked up and gotten dead air, so they hang up.
So it's maybe nearly four months that the dead-air-after-dialing issue has been going on, and about two months that the dead-air-while-on-hold has been going on. It wasn't until my friend shared their experience with my calling them that I realised it's happening on both ends.
Come to think of it, the being disconnected while on hold business might have been going on for nearly a year or more.
I wondered if it was the 15-minute problem I'd heard about, but the time that dead air sets in seems to be random.
It also seems like I'm making/getting more garbled calls, too.
This is possibly (probably?) an ATA problem (Cisco SPA122) but I haven't changed anything in the settings for a long time. I need help in figuring this out. Does anyone know what's going on?