Piggy bank purchase

[nsims]

Hi

Can't get to see piggy bank rewards add to a new phone I want to buy.  Have checked all old posts concerning this but none of these solutions work.  

I sign in piggy bank.  It say u can get £25 off with 100gb which I have more than in piggybank.   With 3 picture device offers links 25,  etc.  When click 25gb find out more it says preorder and shows monthly price but nowhere to add from piggybank .  I can go alway to pay page but still nowhere to add from piggybank bank

Any help thanks