I agree with GIMel. Find a new Dr. You clearly have a conversion issue. And saying that common Hypo symptoms are not hypo symptoms just shows the level of incompetence. He is freaked out by the suppressed TSH.
The reduction from 175 to 25 is in my opinion borders on malpractice.
you can only achieve FT3 in your blood by three methods
1) the amount of thyroid gland production - and with suppressed TSH your thyroid is probably not producing anything. including even the low amounts of T3 produced by the gland.
2) Conversion from T4 into T3. The fact that you have high levels of FT4 but so low levels of FT3 is CLASSIC indication of conversion problem.
3) Direct T3 taken via medication.
The fact that you were taking T3 and had a high level of FT4 but still low range FT3 levels suggests the need to ADD more T3 medication.
I would also agree that a reduction in T4 would make sense but not the extreme reduction that your Dr provided.
Being in the UK makes getting T3 treatment difficult. It is institutionalized nonsense created by the "standard of care" that is taught like a religion to the Doctors that T3 is downright evil and never has a correct situation for use.
Where in the UK are you located?
You obviously need to supplement iron, folate and B12. For iron, 25-50 mg of a good iron supplement should do the job. Best forms are ferrous bisglycinate, ferrous fumarate, or ferrous sulfate. For the B12, you need to get the doctor to increase the infusion, or if not, then you probably need to add 500 mcg of B12 daily. On folate, I read that the recommended daily intake from all sources is 400 mcg, so with your folate level, you need to supplement there also.
Your Endo reduced your T4 from 175 to 25 and also reduced your T3 med, just because of his erroneous belief that your TSH of .02 meant you had become hyper. And now he says that your many hypo symptoms are not due to low thyroid. That is just nuts. There are scientific studies showing that a suppressed TSH does not mean hyperthyroidism, unless you are having hyper symptoms due to excess Free T4 and Free T3 which was not your case. Your FT4 was at 90% of the range, which is more than adequate, due to the high dosage of T4 med; however, your FT3 was only at 27 % of its range. If you were not having hyper symptoms at that time, there was no reason to reduce med dosage. It probably would have been better to reduce your T4 dosage some and increase your T3 dosage. Many of us have found we needed FT4 at least mid-range, and FT3 in the upper third of the range, and adjusted from there as needed to relieve symptoms. You can confirm all I have said by reading at least the first two pages of the following link, and more, if you want to get into the discussion and scientific evidence for all that is recommended.
http://www.thyroiduk.org/tuk/TUK_PDFs/The%20Diagnosis%20and%20Treatment%20of%20Hypothyroidism%20%20August%202017%20%20Update.pdf
A good thyroid doctor will treat a hypothyroid patient clinically, by testing and adjusting FT4 and FT3 as needed to relieve symptoms, without being influenced by resultant TSH levels. Symptom relief should be all important, not just test results, and especially not TSH when taking thyroid med. In addition, there are other variables that can very important to a hypothyroid patient. Those include cortisol, Vitamin D, B12 and ferritin. If not tested for those you should do so and then supplement to optimize. A morning serum cortisol test result is best when in the uppe end of its range. D should be at least 50 ng/mL. B12 in the upper end of its range, and ferritin should be at least 100.
So you need to find out if the doctor will read and accept the info in the link and treat you clinically as described. If not, then you will need to find a good thyroid doctor that will do so. I just noticed you are in the UK, which presents additional problems trying to get a doctor to treat clinically instead of dosing your thyroid med just enough to get your TSH within range, which is the standard of care. If you cannot find a doctor that will do the right thing, then you may have to go private, if you can. If you reach that point, let us know and, dependent on your location, we may be able to give you names of a few private doctors that will treat clinically.