Inew v3 Three Network Call Ending Engaged Dial tone

[elmfield32]

Hi I have been experiencing the same issues with my INEW V3 phone build number cxq_v3_inew_v1.0.4. Been working fine on Three for the last two months, but suddenly stopped working with call forwarding message before ending call. Cannot receive or make voice calls on 3G network, but able to receive data and texts. Switch to Three's 2G network all voice calls work fine, but no data. Been told by three it's phone related, but Simms from other providers work fine. Three deny all knowledge of doing anything and I have asked them to check my IMEI number was not blacklisted, which I was told negative. This appears to be Three UK network related any help guidance or instructions on how to resolve issues much appreciated as this is driving me insane.