Underactive thyroid and miscarried

I have just recently had a miscarriage at 9 weeks. I feel so furious. I've been the doctors the day after I had a miscarriage as I received a letter saying they needed to see me about my blood tests ( I had these done when I was 1 week pregnant and unaware) he then tells me my levels are too low! I'm absolutely disgusted that they did not ring me to get a prescription as I have clearly had a miscarriage because of this! Surely there should be something done about this?! I don't want this to happen to anyone! I was already aware of my thyroid as I was diagnosed years ago and had normal levels for years until this pregnancy.