On web interface of M7350, go to Advance---Wireless---MAC Filtering and you should be able to do that. It also can be fulfilled with tpMiFi APP. But it works for IOS devices only.

Provide the topology pls. Or you may submit a ticket here directly. http://ticket.tp-link.com/index.php?/Tickets/Submit

Good luck~ :)

Are there any restriction rules configured on your W8968? If not, during that time, can you login web interface of W8968 and check WAN section? Is there IP/Mask, Gateway etc.? How about Line Status?

Before upgrade, did you extract it? Any other computers for you to try upgrade?

The speed was tested by cable connection or wirelessly? Can you provide a screenshot of DSL section on Status page of W9980? What's the firmware version of your W9980?