If you want a refund then you'll need to contact 48 support as only they can deal with such matters.
And they don't generally monitor or respond to posts here on the Community Forum.
If you want to contact 48 support then see the links in my signature below.
But if you mistakenly bought two plans then they should both be on your account so you shouldn't lose out even if you don't get a refund.
E.g. at least one of them should be stacked as an upcoming membership plan on your Buy Plan page:
