Vodafine fibre and AX1800 Router

Hi, had Vodafone 900 fibre installed a year ago but had problems with the Vodafone router on  ethernet (new cables that know work but sometimes drops really low and sometimes no connection at all).  Vodafione not being very helpful.  Bought AX1800 to see if  is router issue (and get benefit of wifi 6 mesh around house) but can't get internet signal to router so now no wifi or ethernet  Have disconnected the Vodafafone wifi hub and replaced with the ax1800, input Vodafone username and password (provided by Vodafone) into router settings and tried rebooting several times but still no joy.  Does anyone have any suggestions?  Thanks