I activated a duplicate sim for use with another mobile device, during this I received another phone number. I thought the point of the duplicate sim is to not have an additional phone number, and it should just be a cloned number from the service I already have. With the new number comes an additional charge, I don't necessarily need a new number just a cloned sim card.
Any SIM card will have associated unique phone numbers. But since you activated a DIGITS with Paired DATA (aka DUPLICATE SIM Card), the number that comes with that SIM Card is useless and only needed for a mapping at the back end. You need to go to DIGITS settings in the web page to pair this SIM card number with your actual phone number to make it work. Only then you shall receive your calls and texts to the second mobile device. You are not being charged for that number, rather you will be charged for the service that is provided via the DUPLICATE sim card. It essentially duplicating your phone number, not duplicating your sim card or cloning your SIM card.
Let me know if you have any doubts.
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