@Garyc985 - If you didn't opt for the 'free' (excluding P&P) modem/router from Plusnet, you could try contacting them - quickly - or a better option would probably be to buy your own. Depends on your choice, really.
Hi thank you for contacting us.
As stated there if you did not select the router option this would not be automatically sent, however if you contact us we can still offer the router free within the first 3 months of a contract for the price of postage at £6.99.
I hope this helps.