operating problem with ovulation test

Hi. I bought the advance digital ovulation test. As I had many days of flashing smiley, I thought that maybe it was not working so I bought the regular clearblue ovulation test and I tested both at the same time (after wake-up). After 7 days of flashing, I had a solid smiley (on the 8 day of testing) with the advance digital ovulation test. But the other clearblue ovulation test I tested at the exact same moment showed me an empty smiley.
So my question is what ovulation test is best and is working because clearly at least one is not working (or maybe both!). It's very disappointed, I'm using your brand for months now and your test are very expensive, so they should work. I feel I have wasted my money and my time. Many thanks for your return.