Extend length of time phone rings before voicemail cuts in

I have a Xiaomi Poco F4 and since recently joining Lebara (December) my phone now diverts to voicemail after just a couple of rings. How do i extend the ring time to approx 30 seconds before voicemail cuts in?
Thank you

Call
**61*21*11*30#
Extends to 30 seconds.

Thank you

**61*21*11*30# didn't work for me, but it might be a misprint. What did work was **61*121*11*30# to set to 30 seconds. The 30 can be set to any multiple of 5. To check settings dial *#61#.