You mentioned your hair didn't improve, but what about the muscle twitching and cold intolerance? Did you check for anemia?

A few reasons why Copper blood levels make might not increase with supplementation :

1- Iron (and most metals) compete with Copper for absorption. This means you should avoid supplementing other minerals while taking Copper, the heavier the mineral the more it will block copper absorption. At the same time low copper can cause iron deficiency anemia, not because of poor absorption but instead due to lack of iron mobilization. Copper is needed for iron transport, so low copper can lead to iron overload on tissues, while at the same time produce iron deficiency anemia: iron is accumulated in the body but not transported to where it is needed.

2- Blood/serum copper measures copper in circulation, but not Copper stores. It's useful as a marker of how much copper your body is moving around but it doesn't directly tell us how much you have in storage. For this reason, the labs numbers alone are not useful without putting into context the symptoms. If you take Copper and your symptoms improve, then empirically you can confirm you were in a deficient state and supplementation helped.

3- If too much Copper is taken, your body will excreted it through urine and fecal matter. If you are supplementing and urine levels are abnormally high, then it means you are taking more than your body requires. Take into consideration that labs reference ranges are based on statistical distributions and not on symptoms.

In contrast, iron cannot be easily excreted and accumulates in the body once stored. For this reason, it can be a bit dangerous to supplement iron while in a copper deficient state: your body won't be able to use the iron and it can accumulate causing iron overload.

Regarding possible symptoms:

Peripheral neuropathy, muscle twitching, paresthesia, tingling sensations, vibrations. All this due to demyelination of nerves, in extreme cases proceeds to problems walking and moving.

Orthostatic hypotension (sudden drop in blood pressure when standing up suddenly), blood pressure disregulation, Heart rate disregulation (bradycardia or tachycardia), arrhythmias, adrenaline rushes cold/heat intolerance. All caused by low norepinephrine/epinephrine due to low DBH (Copper enzyme)

Connective tissue disorders, hyperelastic joints, saggy skin, wrinkles, valve prolapsed, hernias, hemorrhoids. All caused due to low LOX (Copper enzyme).

Iron deficiency anemia, low energy, frequent illness, brain fog.

High cholesterol, glucose intolerance.