I need to reactivate my old iphone

You will need to use one of the support options I have posted below.

The primary option (telephone support) under the Apple recommended support link below has not been consistently available recently. So if it is not working properly when you need it, then use one of the other support links I posted below to contact Apple support.

See If you see a message 'Your account has been disabled in the App Store and iTunes' https://support.apple.com/en-us/HT208856. This link says: "There might be a problem with the payment method that you have on file. When you see the message, don't try to edit any of your account information. Instead, contact Apple Support for help.”

Try using the Apple recommended support link above first. But, this site is down/not fully functional very often. Use the support options I give below if necessary.

You can use Apple Support Twitter https://twitter.com/AppleSupport  There may be a wait of an hour or so.

And, if necessary, go here to contact iTunes worldwide support via text or chat https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading, Tell us how we can help.

Does iTunes see the iPhone?

iTunes doesn‘t recognize your iPhone, iPad, or iPod.    

See the Apple Support article(s) below.

Passcode - If you forgot the passcode for your iPhone or your device is disabled.