Purchase Key

Hi Guys, 

i used to work for a Sophos re-seller, recently left and now my UTM at home (SG105W) needs a new key, of course i don't have any ACT or Licenses for it and not working for the reseller any longer they are unwilling to help. I own the kit myself (brought it through the reseller to train at home but actually ended up setting my house up with it too!). I only use this for home use, my wife and I.

How do i get a license key to apply, i expect i will need to pay, thats fine, what do i do first?

Thanks.