Ukash Shopkeeper denied me from geting my ZP :'(

Ok I was looking for a way to get zp, looked all over crossfire website. I don't have credit card and my mobile has a sim that isn't compatible with mopay. Earning free zp is too long and crappy. So i found prepaid cards. I live in the Uk and most prepaid cards are to buy from US so i found only one way i can buy zp. Ukash. I was so happy i took £5 of my mini bank and went to my local costcutter shop.
I said "Can i have £5 Ukash Voucher please"
Shopkeeper: "Ukash?"
Me: "Yeh"
Shopkeeper: "Your under 18 isnt it?"(I'm 13)
Me: I said yh, but there should be a option for under 18 and over 18"
SHopkeeper: "No it's for over 18 only"
Me: " (I said **** you in my mind, but when i saw in website it said 2 vouchers, one fore over 18 and one for under18 then i was confused and went.

Now im writing this and ****ed off. Is there any of you who buys Ukash or ever bought it, and i tried it from PayPoint and if you look here: http://www.ukash.com/media/7964323/ukash-coupon-uk.pdf
it says under 18's are allowed.

My questions:
1. WHich does crossfire accept: over 18 or under 18 voucher?
2. WHy did the shopkeeper say it was over 18 only?
3. SHould i go back to the shop and show the website page?
4. Have you ever been in this situation?

Please try and answer them.