Changed id plan to new id plan. When is it active?

I have been on ID for years, recently changed my plan to a cheaper one. 

Got a new sim in the post but i cant work out when my new plan becomes active or if ill be paying for 2 separate plans or what.

i read somewhere that my new plan could be active within 30 mins but my online account shows its still on the original plan.

According to my online account i have 1 day until the end of the current cycle.

I order my new allowance whilst being logged into my ID Mobile account.

Question: 

When does my new plan start?
Will i be on the same number?
Is it the same sim I've been using for years?

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below is the text and link as it may be helpful to others.
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Once you’ve changed your plan through the iD Mobile app or My Account online, it will change within 30 minutes. This includes your monthly line rental and allowances.  

Even if you change your plan, your billing period will remain the same – this doesn’t change when you opt for a new plan.  “
 

help :)