@Leoz 

Hi, Have you tried to put the SIM Card into the mobile phone and test call forwarding via USSD?

By the way, may I know who Is your SIM card carrier and have you checked whether you have the correct USSD command?

And one more question, did you set up call forwarding via VOIP or VOLTE on the modem?

Thank you very much and wait for your reply.

Hi, on both routers I tried blocking the network in 3g only and in 4g only, but response is the same (MR6500v without volte).
On mobile phone, the code works correctly, but i'd rather not insert and remove the sim every time ;)

Phone carrier is "Very Mobile", a 2nd brand of WindTre (IT)

Thanks

@Leoz 

Hi, I have seen that many SIM carriers required VoLTE feature for voice traffic.

If enabling the VoLTE on the MR6500v, would there be any difference?

@TP-Link there is no difference w/ or w/o volte

thanks