UNABLE TO OPEN MANAGE SUBSCRIPTION AND MANAGE EQUIPMENT PAGE

Your account was likely migrated from the AT&T side to the DIRECTV side. TPG now owns a 30% stake of DIRECTV so AT&T and DIRECTV are now two separate companies. During this process, account management was messed up and thus you are unable to do any of these things. An estimated time for a solution is unknown by us, being we are customers like you. 
If ever you want to manage your subscription or deactivate/activate new equipment, call DIRECTV ( number in my greeting below) and say ‘billing’ to the robot. 

Thank you very much!  This is the most that I have gotten in the past several months.

No problem! Glad to be of help.

I would like to add or remove any premium channels, look at the fees, also reset my equipment like i has in the past, as it stands now, the only control I'm allowed is to pay them.

@ Juniper, thank you

I'm in the same boat - Signing in via AT&T routes me to DTV - then DTV attempts to link me back to AT&T but it takes me right back to DTV again. Ugh. Calling DTV tomorrow so I can figure out why my bundled services bill seems so high.

@KCrazy 

If you are trying to get a discount definitely say ‘cancel’ to the robot as that sends you to the retention/loyalty department where an agent may be able to help you out.