Use dynamic index in holder

I have a scenario where 1 API returns list response. Response attached for reference.

I need to fetch values of subscriberId, responseDate, device, manufacturer, plan, name for each subscriber and add to property called subscriberInfo.

The output format should be: Subscriber: 123 has date: YYYY-MM-dd device: iphone manufactured by: apple and Plan: airtel and subscriber name is: tom

To read the values and transfer to a property I have written following groovy script:

subscriberId = holder["//*:subscriberInfo[1]/*:basicInfo/*:subscriberId"].toString()
responseDate = holder["//*:subscriberInfo[1]/*:basicInfo/*:Date"].toString()
device = holder["//*:subscriberInfo[1]/*:deviceInfo/*:device"].toString()
manufacturer = holder["//*:subscriberInfo[1]/*:deviceInfo/*:manufacturer"].toString()
plan = holder["//*:subscriberInfo[1]/*:plan/*:operator"].toString()
name = holder["//*:subscriberInfo[1]/*:personalInfo/*:name"].toString()

subscriberInfo = "Subscriber: "+subscriberId+ " has date: "+responseDate+" device: "+device+" manufactured by: "+manufacturer+" and Plan: "+plan+" and subscriber name is: "+name

I need to repeat these lines for all the subscribers by changing the index number.

Tried using below script to not repeat lines for each index:

for(int i=1; i<=subscriberListSize; i++){
log.info i
subscriberId = holder["//*:subscriberInfo[i]/*:basicInfo/*:subscriberId"].toString()
log.info subscriberId
}

but this returns null value. holder does not pick up the value of i.

Can someone please help me know if it is possible to iterate over list and pick up values using dynamic index value.