I don't know about Warid deducting money, but its prepaid sim if yes. Then they don't deduct automatically. And since you are first time iphone owner. This is the most common problem.
Its the iphone problem. Lots of services are ON which without your internet package will always deduct your money. And even if you turn ur internet on without any package even for one second. Lteeats data very quickly. But since u said its old sim. Still possible.
And go to settings and in general go to background app refresh and turn it off. And buy an internet package asap.
Same happened to my 3gs when parents bought it and money was used all night due to internet being on but NOT being in use.
Or icloud is eating away your data ( this is next level problem you will face later).