Don't phone. Write.
Tell them that you want the exact reasons why they are declining cover, that you want them to quote the exact sections of your policy on which they rely to decline cover. Point out that unless pregnancy under your particular circumstances are specifically excluded terms, then they have no ground to refuse settlement.
Tell them you expect either full settlement or a "final decision" letter so you can then take it to the FOS.
Don't mention changing flights or anything to do with Monarch, it is irrelevant. If you have to cancel for the reasons as described and they are not specifically excluded (they're not, I have checked policy
here), you're covered and that's that. You'll lose your excess, of course, unless you had excess waiver.
If they persist with their attitude, then off to the FOS.
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If it doesn't get enough funds, it will have to close.
Help them help us, whether it's £1 or £1000.
Holiday Insurance refusing to pay 
