Problem with configuring zone rates - does not recognise options

I could not find the answer to this on the forum, can someone please help?

I have configured Zone Rates but it does not recognise the first 2 rates so it measures everything on the most expensive rate and I cannot figure out why.

My developer set the weight to kg as I'm based in the UK. I have also set max weight to 10000.

Example for zone 1 (but I have the same problem for the other 2 zones). I want to charge £5.90 for weight up to 0.5kg, £7 for 1kg and £9 up to 2kg:

Zone 1 - GB
0.5:5.90,1:7,2:9

I have inserted the weight for one dress as a test at 0.6 in the main description section for the item but when I press the price calculation button it displays cost at £9 rather than £7.

Can anyone help please?

Thank you.

For some reason I solved this by setting Calculation Method to 'item' instead of weight although I'm not sure why this solved it as I want to calculate shipping cost by weight.

However I now have a new problem - if I buy 3 items, each at 0.6kg then it can no longer determine the shipping rate.