Firstly, fill in a form asking for mediation HERE. If your mother is a pensioner do it in her name as it's a lot cheaper.
If mediation doesn't work, take it to the CTTT (but you have to go through mediation first).
Don't forget to go to your next AGM and challenge all the EC members to explain why they are on the EC if they aren't prepared to enforce the by-laws.
The EC isn't there just to address problems they might have and if they're not prepared to accept their responsibilities to other owners, they should get out of the way and allow people who do have some moral fibre to do the job.