I'll use a real life example for this. When I bought a 6s to test the "ecosystem" after my Android dropped "dead", it took 15 hours to activate iMessage. When I exchanged that for a 6s Plus, before the 14 days were up (paying the difference), it took 12 hours. When I bought an 8 Plus, it was instant.
Here's the caveat: I have international texting enabled on my plan from my provider. So all those "requesting activation" didn't cost me a dime. But this was before the network on my provider (Freedom Mobile in Canada) was approved by Apple (6s and 6s Plus, both 128GB versions). The 8 Plus (256GB version), was bought after the network was approved. In addition, since I retain my 6s Plus, the settings were transferred over setting up the 8 Plus. So I may or may have not had to go through the "reactivation" procedures.
But what you are implying is that Vodafone charges for this and Jio and Airtel does not. Maybe you should contact Apple, but then the "revolving door" will start. Pinpointing the blame will be difficult to do.
The UK activation number is not blocked is it? If you're getting charged, then it's not.