Yup - same situation - I was told only last week, you have 2 options
A) sign up for DD - no deposit required
B) pay on time for 14 months (I think it was 14) and get your 300e returned.
My query with them was how do i get my 300e back - and that was it - if you pay your bill on time for circa 14 months, they will refund you in full OR let you use it to pay future bills.