Re the speeds... is the ~500 on an ethernet cable connection or wifi? If wifi then that is the maximum speed you will get on a wifi 5 router (Hub4) - if you connect 2 - they should each get ~500 = 1GB ! You need wifi6 equipment to get near to the 1GB
Re the cable you might get VM to supply you with a 3m CoAx cable as they do have them - but they may want to do a Tech visit for that as it "could" affect the power levels to the Hub
You are not permitted under the T&C's to use 3d party (inferior) cables as they can and do (as I have discovered myself) introduce noise into their Network which affects others connected in your location - if they discover that they are entitle to bill you for the cost of any repairs.
Just get rid of it
The other option would be to leave the Hub where it is - put it into modem mode and get your own wifi6 router (for the faster wiffi speeds) and connect it where you want in the property with a run of ethernet cable
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.