This forum is for customers of BT phone and broadbandl. Plusnet have their own forum, as your issues may be specific to their equipment. As you are no longer a BT customer, please could you post on their forum.
The only support for that product, is via the helpline number that came with the product. Nobody on this customer to customer forum would be able to help, as its not a BT Phone or BT Broadband service issue.
We are all just BT customers here.
If you look on the Plusnet forum, you may find someone else using the hotspot 500.