Spent the last hour searching but cant find the answer!

I purchased £500 worth of 3v vouchers yesterday at Tesco Dalkeith. I was charged £500 and got the points added just fine.

When I got home I found that only 14 out of the 20 cards were activated and I only had 14 activation slips.

Whats Tesco's likely response when I take them back and ask for replacements.

Can they check their systems for the non activation or am I likely to get a fraud suggestion?

Is there something I need to say or do to assist me?

thanks