I have had premium bonds for more than 50 years. I've never won anything.
The minimum prize is £25 and the prize fund is an equivalent annual interest rate of 1.50% (now, but it's varied in the past).
£25 at 1.50% compound interest for 50 years is £52.625, so with £25 you'd, on average
1, win every 50 years.
If you have any more invested then you've just been unlucky.
My £5 I've had since birth has won nothing.
1. On average of course...