That is only your estimated bill, it doesn't recognise any corresponding credits etc. and is often considerably wrong. Personally mine is more often incorrect than correct. You are unlikely to have a £900 bill.
Essentially sometimes when you get a new phone this will have an equipment charge to link the specific device to your contract and then this amount is credited back in time for your bill date. The intention is not that you will pay this amount, as you will pay your monthly amounts instead of the full cost, and most customers don't ever see this or notice it as it gets covered on the bill.
It is a so-called "equipment charge" of £823.56 (which will be the approximate value of the handset), but this gets covered by EE and then you take on your normal monthly payments.
Any further discrepancy outside of the £823.56 charge will likely be pro-rata part charges based on when you upgraded in relation to your usual billing date. Part charges are to reflect when your changed from your old plan to your new plan in the middle of a billing cycle, and charge you for the days accordingly and the month ahead.
Your agreed monthly amount will then be present on your next bill.
Other numbers appearing on your account could be if you have ported across a number recently, or have a watch plan or a tablet plan linked to your account. Any connected device with a SIM Card/mobile connectivity will have a number associated.
If you want to check the equipment charge or talk through any concerns you have with your account, you can give EE Customer Services a call on 150 and they should be able to put your mind at ease.
