First of all, see if the forum staff can sort the request. If they can that'll be quickest and easiest. The IMEI will be somewhere in VM's data pile, whether it's readily accessible I can't say.
If they're unable, then you may want to make a subject access request. Whilst VM might not actively retain the IMEI, it's not guaranteed, but pretty common for it to feature on phone invoices, so asking for device data, legal correspondence.
If these were (say) your and your partner's personal phones, can you get witnesses who will confirm that your phone was not the one returned by Likewize? That's not definitive proof (because that doesn't confirm what you sent to Likewize) but it's useful circumstantial evidence.
You may also want to consult Citizens Advice.