Hey mate,
I don't know if you're going to see my message,
Testi is a good app to grab test dates.
If you already have signed in with your license number and the pass test certificate number,
Then you click onto the option saying "no available test" bar and takes you into the 2nd page showing two option:
Type in your post code
Your test date (old one that was cancelled because you had to retake the theory test)
When you're on that page,
Click the Gov logo icon, it'll take you to search bar and then type driving test and then type in "driving test"
It works because it doesn't record your cookies and can get the test dates on Monday.
Do not call them in the morning, you'll be stuck in traffic.
They'll be released across the UK and it'll be a large traffic when using the laptop for these dates.
I hope this helps, :)
That's how I was able to get my date.
Also have your bank card ready in advance and type your license number and theory past test number in a Google doc app, so that you can copy and paste it.
You have until 06:20 to get a date maybe less.