Landing sync placements is a tricky beast. Sometimes there’s no science or logic to it whatsoever and the most unlikely tracks end up on projects which you least suspect.
It’s important to keep plugging away, either by making new and better material, work on interesting covers or picking up new catalogue to pitch so you have the best shot at landing something. A lot of it is down to timing and luck. You need to do your research, target supervisors directly and show that you’ve not just blanket emailed them along with 200 other people. You can find a lot of info online about what shows are coming up, who supervises them etc. Write to them on Twitter, many UK supervisors are open to this and want exciting up and coming music (such as Made In Chelsea).
Having worked both as a supervisor and a sync agent I know that the key things are to pitch effectively, build relationships, understand your ownership rights, attend conferences and get facetime with people. Meet up and coming directors and let them use your music for free if you’re starting out. Compare your music to acts you aspire to before sending it out, if it’s not to a high enough standard it’s better to wait as it’ll just end up in the trash.