You said this:
I didn't check the message till this week, assuming it was a typical "hi it's mom call me" message.
If you saw that she had left a message, I think you should have listened to it. If I realized that my kid was ignoring the substance of a message I'd left for them, and making assumptions about what I said, I'd be a bit peeved. Basically, that's ignoring me. I don't buy that you truly didn't have time to play it once you saw it. So yes, I think that's rude.
I'm sure I'm influenced by the fact that I don't reach out to my college-age kid "just to talk." If I try to reach her, there's something specific behind it ("do you want to be there when we pick out the new cat, or can we act without you?" / "Your tuition payment is ready for you to authorize to the college").
And I either need an answer, or I need an acknowledgment.
Were I your mother, if I said, "call me back," it would be because I had something specific to say to you. (Of course, I would never just say "call me back"; I'd say, "There's a party for your uncle on Saturday--call me to get the details"--I never leave a message about calling me back that doesn't *also* have info in it.
Maybe your mom calls just 'cause she wants to chat, and so maybe a majority of her voicemails aren't about anything specific and are literally, "it's your mom, call me back." But I do think it's bad form to *see* her voicemails and not *listen* to them. I also think it's rude not to return people's phone calls, especially if they person has said "call me back"--that's an old etiquette rule, from the time in which every letter was supposed to be answered by a letter (unless you wanted to sever or damage or dial down the relationship
In my situation, I might leave a message to my DD with info she needs, and maybe I don't need to have that acknowledged, but if so I usually say that. And I think that when the message is, "your tuition is ready for you to pay it," she should say, "got it."
I'm wondering if it possibly came across to your mother that messages from her are not very important to you (and, thus, by extension, she is not very important to you).
Me, too. And I would say that you need to never, ever, ever say to her "Oh, I saw your message, but I assumed it wasn't anything important so I didn't listen to it." You've said it to us, which is really like not saying it to anybody (because posting stuff on EHell is sort of like talking to yourself--we're ultraprivate). So maybe you didn't say it to her. But don't ever do so! And from a Character point of view, I don't think it's a valid excuse. This is someone you want to be in touch with--put forth that small bit of effort.
I'll admit that my personal experience is saying that I think people should provide a way to be in touch that *works*. If you don't want people to contact you via voicemail, turn it off. Or, if that's not possible, do as mentioned above and change your voicemail message to say, "I don't listen to these messages; please text or email."
Or sign up for Google Voice, and give your mom that number--then you can set it to convert voicemail messages to texts and send them to you. They'll be mostly gobbledegook, but you'll get enough of the message to realize mostly what it's about.