Quite a late answer, but the reason behind this is because you probably played on SP before joining MP, and MP's game time is completely different and not related to SP game time as it is constantly running. So the reason behind this doing is your SP was 300 days behind the MP game time, and in those 30 days that got skipped your drivers probably earned your a hefty 40 million. So I doubt there is a way around this unless you make a new account (based as much as possible off mp time) and hope that this doesn't happen again, that is of course if you don't like the outcome
Again sorry for the late reply, only just seen it on the help section, have a good June
Fading.