So that they can liaise with your old provider to port your number over?
It's standard practice for all providers to request such information when dealing with number porting requests.
In most places, like Europe and many other countries, the process is "recipient-led." This means that when you want to switch to a new network, you contact the new network (the recipient). The new network then asks your current network (the donor) to transfer your number. This method is generally seen as straightforward for customers because they only need to interact with the new network.
In this case the new network (48) needs details of your account in order to request the donor network to allow your number to be ported over.
Account number is usually only required if you were on a bill pay account.
Not if you were on prepay.
If you need to contact 48 support about this then see the links in my signature below.
