90% maternity pay for 6 weeks - underpaid or not?

Hi there
Apologies if this is in the wrong place.

I am currently on maternity leave from work where we receive the statutory 6 weeks at 90% and the remainder at £135 or whatever it is.

I got paid yesterday and was expecting more or less my normal salary for the month of march - i worked 2 "normal" weeks of the month and then took my first 2 weeks maternity at 90% - so i should have more or less full pay for 2 weeks, and lose only 10% on the second fortnight.

We get paid every 21st of the month, and i began maternity on the 8th. My normal monthly salary is £2333.33 before tax, 1657.77 after deductions. So i think, weekly i take home £382.58 after deductions.

So surely i should have something like £382.56 + 382.56 + £351.76 + £351.76 = £1468.64

But i only received £1300??

We don't have a payroll dept or HR and I don't work at head office but from a smaller one in wales, i've already rung to query and they said they will get back in a fortnight!

In the meantime can anyone help me - maybe i am calculating something wrong? 150 pounds would be very helpful right now!

Thanks

Can224