My son who is now 22 was also diagnosed with a hemangioma in his foot when he was little and the diagnosis was incorrect. He had an AVM. I do feel like the delay in the diagnosis impeded his health.
You need to find a specialist in the field of Vascular medicine to find out treatment options. There are wonderful doctors and the internet is a great tool for research. At least, you will find others experiencing the circumstances as you and your child and learn options available to you.
I am available for questions, it needed. I will say a prayer for you and your child.
Polly Morgan, Son Adam