I don't think the BBC do call Hamas a terrorist organisation. They might say something like "Hamas, designated by the UK government as a terrorist organisation" which is true - the UK government does have that designation. That isn't the same thing as the BBC calling Hamas a terrorist organisation.
Also the BBC might not always get it right but I think they do aim for impartiality, and I think they do a good job most of the time. People on the far-right think the BBC is too much on the left, and people on the far-left think the BBC is too much on the right.
