don't know what this local hub thing is (or where you are) but that sounds a bit crap.
the poll card i got says you can apply for a postal / proxy vote, but doesn't say where / how, although it has a phone number and web link.
it does say that deadline for requesting a postal vote is 18 april, so you don't have that much time.
suggest you go to your council's website (if you're somewhere there's county and district councils, then it's the district or borough or whatever - the one that sends the council tax bills) and there's bound to be a page for it somewhere - possibly under a heading like 'your council' or 'council and democracy' or something.
alternatively, i've just tried my local council's and it leads to a national government website with a form for applying for postal vote
here
although you need to print it out, fill it in, then get it back to your local council.
if printing isn't practical, then you'll need to phone up your local council to ask for the form (assuming that getting one from local council office or whatever isn't possible.)
if this local hub thing is council, and they are effectively disenfranchising anyone without web access, then that wants a fuss making about it.