I'm Stupid coz Table Rate wont Work

I am obviously doing something completely wrong because no matter how I set up the table rate values, when it comes to checkout the customer gets a shipping bill 50 times bigger than it should be ??????
This is the table I have set up in Grams........up to 500 grams = £1.90 and so on.

500:1.90,750:2.89,1000:3.89,1500:5.59,2000:7.29,3000:9.69

I sell a bag that has a weight listed at 1500 so that should be £5.59 + .75 Handling, which is a total of £6.34 yet the price quoted comes up at £285.75 !!!!!

Where the hell am I going wrong.

Zen Cart ver 1.3.1

I think the table should read in kg, and not grams:

0.5:100,1:200,1.5:300 etc

Have tried that also, end result is not as drastic but still not as per table.

0.5:1.90,0.75:2.89,1.00:3.89,1.50:5.59,2.00:7.29,3.00:9.69

Bag sold at 1.5kg should be 5.59 + .75 handling should be £6.34 but is coming out as £10.44 ?????

More help needed I think which will be gratefully received.

check your tare settings located in
admin > configuration > shipping & packing

Also check the:

Enter the maximum package you will ship

If the value is under 10000 (10kg) it will try and pack your order into X boxes and charge double/triple postage, according to the number of boxes as set here.

Because your table is in grams, you'll need to put a gram figure in here.