Whatsapp call (and Zoom conference call) issues on Plusnet Fibre

[#1]

I am on the Unlimited Fibre Extra contract and I have had an on-going problem with making Whatsapp calls. When I am on a Whatsapp call, on my phone, at very frequent intervals I am interrupted with a beeping tone and the message "Reconnecting" appears on the Whatsapp screen. This is proving rather disruptive. I am convinced that it is a problem with my Plusnet broadband because when I disconnect the wifi feature on my phone, I am able to have a long uninterrupted call on the mobile network.

I have also tested the same with my office wifi; and also never had these issues with my previous ISP which was Sky Broadband.

I have also splitted bands (2.4 and 5 Ghz)

I copied content from an earlier post and have tried to reply to all the queries as I am having exactly same issue (https://community.plus.net/t5/Fibre-Broadband/Constant-reconnection-issues-on-Whatsapp-calls/m-p/144...) .

I have though noticed less of issues if I use VPN on the device before initiating the call. 

Can someone from Plusnet provide a fix

[#2]

Have you checked your speeds for download and upload?

[#3]

Well above the requirements - 37.22 Down and 6.64 Up

[#4]

Had a chat with Plusnet Tech support, and the person on the other side kept saying since broadband is ok there is no problem on our side.