How do I Reduce The Risk or Stop SIM Swapping Attacks?

Google Fi, and Mint Mobile are two MVNOs that claim to prevent again sim swapping [0][1]. Mint Mobile offers TOTP, and Google Fi is linked to your Google account, so you can add U2F/TOTP MFA. However, it's still possible for a T-Mobile retail employee to hijack a Google Fi, or Mint Mobile number?

Both MVNOs use T-Mobile for their backend, but Google Fi uses US Cellular as well. There have been documented cases of retail T-Mobile employees conducting sim swaps. There has also been documented cases of Mint Mobile users getting sim swapped [2][3][4][5][6]. So, are MVNOs really not vulnerable to sim swapping? Are VOIP services like Google Voice the only secure alternative to prevent sim swapping attacks[7]?

0. https://support.google.com/fi/answer/9834243

1. https://old.reddit.com/r/mintmobile/comments/jw21qf/how_does_mint_prevent_sim_swapping/

2. https://old.reddit.com/r/mintmobile/comments/113dyvi/sim_swap_a_few_days_ago_day_3_of_still_not_having/

3. https://old.reddit.com/r/mintmobile/comments/t4g4g3/i_just_got_sim_swapped_and_im_terrified_this_was/

4. https://old.reddit.com/r/mintmobile/comments/nw4gth/just_got_sim_swap_hacked/

5. https://old.reddit.com/r/mintmobile/comments/jw21qf/how_does_mint_prevent_sim_swapping/

6. https://old.reddit.com/r/GoogleFi/comments/10qes3h/at_least_one_google_fi_customer_had_accounts/

7. https://krebsonsecurity.com/2018/11/busting-sim-swappers-and-sim-swap-myths/