If you don’t qualify, then you don’t qualify.
Essentially the biggest difference between SMP and MA is that you don’t receive the first 6 weeks at 90% with MA, otherwise it’s the same if you qualify for the full amount.
I don't qualify for maternity pay at my job as I started 1. Day. Too late to qualify. There's nothing I can do, i offered to swap holiday for an earlier start date or use holiday to 'pay in' and other various things. They wouldn't have any of it and they're legally fine to do this. It's just business.
But it did show me what kind of company it is, and tho I dont actively do anything against them, I also certainly don't feel like going above and beyond for them either.
Check the gov website for eligibility for statutory maternity pay. You have to have worked for 26 weeks before you are 25 weeks pregnant essentially. So you need to have been on their payroll before you were pregnant. But if they are correct and you don’t meet the eligibility for SMP then you can get maternity allowance but there’s nothing you can do.