I was offered a free 5GB SIM when I got broadband. I started using this to hotspot when Virgin took several weeks to install broadband in new flat after moving. What they didn't tell me was that I would rack up huge charges after going over data limit. At no point was I told this. Now the website won't even let me add on data to limit these costs. Customer service was better, and easier to reach, with EE. So I'll consider moving everything to them now.
Welcome to the Community Forums. I'm sorry to hear that you've not had the best experience since joining Virgin Mobile.
When the team set up your new contract, they will ask whether you'd like to set up a spending cap on the account, which you can set to 0 if you do not want to go over your data usage and incur any extra charges. You can find out more about spending caps and how to add them on here.