Not getting calls, texts, or voicemails in a timely manner

I've been an AT&T customer for ages and have had this problem for years, but it's getting

so bad that I will have to switch carriers if it's not fixed.    In short, I don't get voicemails and texts when they are sent.  I might get them a week later, but I do not get them when they are sent.

Sometimes I don't get calls when they are placed either---  they person will be put through to

my voicemail and I have no notification that they have called.  And because I won't get the voicemail until several days later, I generally find out about this by accident when I actually see the person who called, and they tell me they were trying to reach me.

The most absurd example of this happened last week.   Someone dropped something off at my house on Sunday.  On Friday, I finally got their text from Sunday morning:  "HI! I just dropped something off on your porch!"

At&T customer service acts surprised and saddened that I am having this problem, and has no idea what to do about it.   Just wondering if other people out there are having this problem as well.   I have had this problem with an AT&T contract, without a contract, and with a number of different brands of phone.

Please respond if you are experiencing a similar problem!  Thanks!