Tax credits

[Tillylils]

Really hoping someone can help me as it's impossible to get through to the tax credits helpline.
I've just received my tax credits renewal. My circumstances haven't changed but my tax credits have increased. On the part that states my income it says that my employer has provided the figure, but it's quite a bit less than my gross annual income. So is it the net income that they use?

Any pension contributions are taken off.

So gross minus pension contribution

That still isn't right. My gross pay is 18000 and it says my employer has told them 12000.

is this a new job or a job that you have been in less than the tax credits tax year?

Phone between 2.45 and 3.15 you will get through.

It's the same job, same money, haven't had a pay rise for years. It's strange that they've gotten that figure from my employer.
It's difficult for me to ring during the day as I'm in work but I'll have to try.

Sorry for asking under this post but can anyone help .on renewal form when they asked for other income and if it is less than a pound should I put 0 or leave it blank. On the websites they written what to include over 300 and what not.but on the working sheets it is if it is minus figure enter 0. So 0 or leave it blank ??