Is telephone conferencing blocked in Japan?

I have used telephone conferencing multiple times in the past in my home country (mostly before SNS used to be the norm for calling).

However, in Japan I feel its need when I am on phone with some customer support and they can’t speak English and I can’t understand fluent Japanese. So I tried adding some local friend to the call for helping with translation, but I can’t seem to “merge” these two calls. I can “swap” and talk to two people on the phone in sequence, but not in parallel. I have tried with different sets of friends as well as different mobile carriers, never been able to merge the calls.

Has anyone done any conference calling in Japan successfully?

JFYI, primer for those who don’t know what a conference call is – https://www.indeed.com/career-advice/career-development/making-conference-calls-with-cell-phones