billing too much.

i recently upgraded to a samsung j5 i was told o will be billed 299 month end only to be billed 1007.i went to maponya mall store to lay a complaint.i was told the reason for being billed this much was that i failed to cancel the contract of the other phone.that i dont mind but the problem is i have paid 409 for that other phone but there are no data bundles nor airtym on that phone.what was i paying for?can somebody please explain.