Seriously – it’s still not enough detail to provide you with advice.
:sarcasm:
Are they performing well for your site?
Are you seeing good returns?
Are you having any other problems with them?
But I would say that if you don’t think that it was a “misunderstanding” – that they simply will not honour an agreed term – then you will have to consider whether you trust them to stick to this contract.
However, a 50% deal is unusual and a 30%-40% rate is more normal.
Without naming the company – and without discussing in detail – then you’re really asking an unanswerable question.