my att cl82309 landline (wireless) is blocking ALL incoming calls.

To the OP what makes you think your phone is blocking all calls? Are you sure it's not a trouble on your line. Here's the manual for your cordless phone system, it doesn't have blocking abilities. 

The caller to my landline receives the message "Your call is blocked". My provider account shows all functional on the phone, no blocks Also CS said Spectrum Call Guard only rings busy or "not currently accepting calls".

Don't know what to tell you, read the manual provided, your phone doesn't have the ability to block calls. You said "the caller" I thought all calls were being blocked. If you have another phone, try it than you'll know where the issue lies. 

Spectrum call blocking looks like you can access it yourself online to see if anything is activated. I sure wouldn't trust what someone in a call center tells me if I've got the ability to check it myself. 

I received a return call this am from drive.ky.gov on the AT&T landline but my sister texted to the track phone she loaned me that she is still receiving the message "this number is not accepting calls because they are blocked". I had removed Spectrum's Call Guard before both calls. I only have two of the three handsets that came with the CL82309.

So just one number is being blocked? Need to know the real scoop to give you a decent answer. Again your phone CAN'T block calls and the number of handsets doesn't matter.

Have you tried another phone? 

I have not tried another phone yet, but will try that. There is only one line for the two handsets, both of which allow dialing out but the only incoming call I've received was a callback from drive.ky.gov re: a change of address on my license. I presume it was allowed as a governmental #, such as 911 or emergency notifications. Thank you for your input and suggestions! Seems a case of planned obsolescence.

There is only one line for the two handsets. 

Yes, that's the way cordless systems work.