I've had exactly the same issue, a 7.5 in listening which I need to increase to 8 to secure a score for an ITA. I ran a
quick search on-line and it's clear that sending listening and reading exams for remarking is pointless as the answers are not subject to subjective evaluation, while writing and speaking definitely are. I would just recommend that you just retake the test - I know, it's a pain for your wallet and a quite a big change in any timeline that you might have in your mind but it's the only way. I took my first IELTS on the 10th of February and I'm resitting the test on the 24th of March just to increase my listening score to 8 which will secure me an ITA. Good luck!