Limit is not checking the exchange rate

Hi, I am trying to do a top up which I do all the time. I have a yearly limit of £12,000 I have used £1,300 so have £10,000 left. The top up comes from ZAR account. The amount I am trying to top up is ZAR 50,000 which is £ 2,900, but it keeps on saying that it is over the £12,000 limit. I think it believes it is £ and not ZAR, what can I do??
Mark

Take a look at Wrong top up limit, always considering Euro it is the same problem.