I honestly don't know what you're getting at, but you're arguing with cold facts. £3bn contribution, £0.5bn cost -
No, I'm arguing with your quoted stats. A little thought shows that it's an impossibility for every immigrant to be a net contributor as you allege.
Anyone who isn't working and earning a good wage will not be a net contributor, and that category also includes anyone of school age, past retirement age, the ill and sick, most mothers/carers of young children, the unskilled and unemployable, anyone illiterate or not fluent in English, etc etc.
Also, education to GCSE level costs around £70,000 per child. Like I said, most of us - you included - will never pay off what you've taken before you die. It's probably not nice to hear that most immigrants come to the UK and pay for their stay while you (and me, and most of us here) are a burden on the taxpayer, but it's the truth.
I can't believe you can't see the obvious flaw in your own argument; so you say most of us "won't pay off what we've taken" but many/most immigrants have/will have children and will expect them to be educated (rightly) but somehow they'll
still be "net contributors" and that's before we start on other costs incurred or benefits paid.
Maybe you need to read what you've written, or stop believing the hype?