I joined Plusnet on April 9th. I still hadn't received my email to claim by £75. Joined this group and discovered I was not alone.
I messaged Plusnet on Facebook messenger on 28th asking when I could expect my email. Josh answers two days later, 30th April, and said he had claimed my reward for me.
I have just received a cheque for £75 today 11th May. Pity I can't get to the bank!
Hope this helps someone . (Put your username in the message).