tallulah100 I had exactly the same, my FT4 got up to 30 with a suppressed TSH. My then GP allowed this because she was 'sympathetic' to my symptoms. Then she retired.
New GP freaked at suppressed TSH but by then my FT4 was just within range as I'd reduced my Levo slightly. But she wasn't concerned about FT4 (and FT3) being in range, she is TSH obsessed.
So rather than fight a losing battle, this is when I came to this forum, read about optimal levels of vitamins and minerals, adrenals, etc, and set about testing. I discovered that most of my vitamins and minerals were deficient (only B12 anything like reasonable) and a problem with adrenals and sex hormones, plus rather poor T4:T3 conversion.
After addressing all those problems I now realise that pumping more and more Levo into me (200mcg at one time) which resulted in FT4 of 30, but still very symptomatic, was not the answer, it was just making things worse.
So my suggestion would be as a first step test (if not already done)
Then post the results on the forum for comment.
It would also be a good idea to have full thyroid tests to include
Thyroid Peroxidase antibodies
All these tests will give a full picture of what is going on.
You are unlikely to get them all done through your GP, especially FT3 and Thyroglobulin antibodies. So if you can find £99 your best bet is to do a private fingerprick test at home which includes everything.
If you can manage a bit more, although a venous blood draw would be needed, then including reverse T3 could be a good idea as your FT4 is so high you might be making rT3 and not enough FT3.