Welcome to Vodafone Community
check that you have your subscription user name and password before buying a new modem.
Get it from the chat with customer services.
I used a TPLink VR900 but it had issues with keeping the 24GB band operational and nobody at TPLink could solve the problem. Now I use the VF bradband modem without any problem.
My speed is as per T&C . I did change the DNS servers and keep my 2.4 and 5GB wifi networks separate.