Inept Strata Management company

We are only a strata plan of four units, so probably don’t register as very important with the company that manages us. Last year they suddenly stopped sending us notices for our quarterly levies and, as a result, we went into arrears. The company has started charging us interest. Is it entitled to do this? And where does the interest go – to the company or into our sinking fund? Also, three of us were in arrears at the time of the AGM. Were we eligible to vote? In which case, are the minutes of the AGM null and void?