Let's put it this way, they looked at your account and were simply paying out more than taking in. They had a few choices they could have made, they could have started shaving some signups off your account, terminated your account without pay with the reason that your chargebacks were too high or paid you until now and ask you to no longer participate in the program.
Nearly every program out there would pick the first two options. You should thank them for getting paid and for their honesty that they could not make a profit from your traffic.
my
WG