Over the last couple of months I've made a few balance transfers from another credit card. I thought there was a 0% offer for 12 months with an up-front fee. I go to look at this month's statement and I've been charged interest.

The interest charged charged is as follows (pasted from statement):

Balance Transfers 1.714 % £ 17.93 £ 1,889.75

This is not the all the transfers, just the most recent one. I didn't notice this charge when clicking through the pages, and I expected the same arrangement as the previous month.

What has happened?