Upvote:2
The above sentence, tells without doubt that I did not have the virus when the test was done, which is September the 8th, which means that I have not contracted the virus from the contact that NHS informed me about, because it was on September the 7th
That's not exactly what it means. It means the virus was not detectable on the 8th but even if you caught it on the 7th, it would not be immediatetly detectable. While the NHS fails to provide specific advice, there are many countries where it is or was recommended to wait 5 to 7 days after a contact before getting tested.
Therefore I think there should be enough evidence that there's no reason for me to self-isolate or take another test.
From a purely legalistic point-of-view, both the advice you received by email and the NHS website suggest you should take a test upon receiving the notification. That's the plain meaning of the text, all your travel history, the date of the contact, and any test that you took in between are completely irrelevant from this perspective.
Apart from the rules, taking a test a few days after a potential contact makes more sense than taking it immediately. That seems to point to the same conclusion as far as I am concerned: Even if you are exempt from self-isolation, you should get a fresh test, probably on Monday or Tuesday.
Note that it's also not obvious you are exempt: your vaccine wasn't administered through a UK vaccination programme and you haven't received a full course of either vaccines you received. To the best of my knowledege, the AstraZeneca + Pfizer combination hasn't been approved and is not routinely administered in the UK (i.e. outside of clinical trials).