I find it odd that your readings were as you describe, if one is over and one is under, the police take the lower of the 2 readings - which should have meant that you were under and no further samples can be provided. You cannot be required to provide more than 2 samples of breath. (Unless you mean by a "fail" that you did not provide a proper second sample. Even then, the police can only restart the machine to obtain ONE more sample, so they have 2 in total.
Then if you provided 2 which were inconclusive, I presume you mean between 40 and 50, which then meant that you were offered a blood or urine sample. It would be very unusual for your blood sample to come back at about 200 (2.5X the legal limit) - unless you had been drinking quite a lot shortly before the breath test procedure which then elevated your sample. (50 in breath is about equivalent to 120 in blood) what was the delay between the breath tests and the blood sample being taken? What were the readings from the ones that were 'inconclusive'?
When the police released you pending the blood result I would have expected them to bail you to return to the police station at a fixed date. Did they not do this? If for some reason the police did not do this, I would have expected the officer to phone you, tell you the result and then say: "please come to the police station at xx time and date" for you to be charged with the offence.
If there was a delay between the breath and blood samples, and you had not been recently drinking (the difference between 50 in breath and 200 in blood is about 5 units) then I actually think that you may have missheard the result over the phone, and the blood result was under.....
You mention about why your car was not impounded as 'evidence', that would normally only happen with a serious injury collision. Was anyone hurt at all? They would not seize it for a damage only one.
Just sit sit tight for another 6 weeks or so to see what comes through the post. Certainly do not phone the police as that may stir up something that would have gone away otherwise. After that you should be in the clear.