Here are my thoughts on high B12.
1) There are diseases associated with high B12. They are liver disease and bone marrow diseases. Have they ruled these out? (Not all bone marrow disorders cause high B12.)
2) False high B12 serum levels can be a result of b12 supplementation. If you are taking a multi-vitamin or B12, the result will be higher than if you weren't supplementing. It is best to stop all supplements 4 to 5 days prior to checking nutritional status to get a more accurate reading.
3) MTHFR genetic mutation can occur where your body cannot convert b12 into a usable form. If your body cannot utilize it, you can see elevated serum levels. And if you are taking B12 in a supplement, it is usually the one that requires your body to convert it. And if you can't, well then you'll see elevated levels.
You can ask your doctor to check for this mutation. They should also look at your folate levels, MMA and homocysteine. Many times folate is high too. I would look at the symptoms you are experiencing. Basically, you would be having symptoms as if you had a b12/folate deficiency. If you doctor is not familiar with MTHFR mutations, you can get that tested on your own. Of course insurance doesn't cover it but it may be worth finding out.
http://mthfr.net/read-this-first/2012/01/25/