mobile phone +£40 airtime for £20

i ordered this
http://direct.tesco.com/q/R.202-3677.aspx
for £20

says if you add £20 airtime voucher from link on the right first the fone is free so i did that and went through to check out and payed £20

This is the status of my order

# 1 x Tesco Mobile 10 Airtime Voucher(At warehouse - dispatching soon) details
# 1 x Tesco Mobile 10 Airtime Voucher(At warehouse - dispatching soon)
# 1 x Tesco Mobile Motorola F3 mobile phone(At warehouse - dispatching soon)
# 1 x 20 GBP Tesco Mobile Airtime Voucher(At warehouse - dispatching soon)


notice anything? Apparently if you buy a fone off tesco at the moment they give you £20 credit!

So as long as thats right thats £40 credit AND a fone (all be it not the greatest) for £20
That has to be a good deal!

oh it charges you £4.85 for delivery but deducts it at the end as delivery is free on ALL fones

Order Summary:
===========================================
1 x Tesco Mobile Motorola F3 mobile phone
£19.97 (1 @ 19.97 each)
1 x 20 GBP Tesco Mobile Airtime Voucher
£20.00 (1 @ 20.00 each)

===========================================
Subtotal of all items: £39.97


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Delivery charge: £4.85
Subtotal before Promotions: £44.82
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Discounts & Promotions
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Buy Tesco Mobile Motorola F3 + £20 Tesco Mobile Airtime voucher and get this phone free
Promotion value: -£19.97


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Total discounts: -£24.82

Total to pay: £20.00
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Total to be taken from your credit card: £20.00