Credo che sia stato tradotto male in italiano, almeno il punto 14.
in inglese menziona:
remaining monetary amount IVA esclusa è il credito residuo secondo me(1) to limit the usage of regulated retail roaming data services at the applicable domestic retail price with a pre-paid subscription to the volumes that can be bought at the wholesale roaming data cap by the remaining monetary amount, excluding VAT, available on that pre-paid subscription at the time of the roaming consumption.