Calculating maternity pay

I got paid today and was paid over ??300 less because they'd changed my tax code due to me doing a mystery shopping job and the tax office thinking I had two jobs! They have said I should get it back next month after I told them I only earnt about ??20 with the mystery shopping but with me being 22 weeks now this wrong wage is going to be included when they calculate my maternity leave isnt it?



I only get 100% for the first 6 weeks but Id rather it was 100% of my real wage and not a botched up one!