If they are cheating your client, they are cheating everyone.  I just looked at a notice that a client received. It shows interest from April 15 through June 16, a period of 62 days, figured at 7% per annum with an interest factor of 0.011960229.  I don't see how they get this number, but maybe it is from daily compounding.  

For 14 days, June 16 through June 30, they show the interest factor as 0.002688281.  Then for 80 days (June 30 through September 18, it's 0.015459272.

This is the kind of systemic problem that TAS is supposed to resolve, but they will probably show no interest.