Power of Attorney - can it be cancelled?

[NMFP]

Hopefully it won't come to this but my brother and I share POA (jointly and severally) for my mum and it isn't working out.

I look after her affairs in practice but he has ideas about her money which he refuses to talk through with me. He will call her up and try to persuade her. Nothing in writing or emails. She doesn't want to upset him, and seems to be relying on me to control the situation, which is hopeless because he isn't communicating with me.

So, in principle, am I stuck with this?

What type of power of attorney is it, an enduring one or Lasting Power of Attorney, and has it been registered at the Office of the Public Guardian?

Its an LPA and yes it has been registered.