That table partition is on some datafile belonging to some tablespace right,

Resize the datafile , increasing it.
Also if the number of extents has also reached 505 , modify it to have unlimited as for now, but i would suggest to reorganize it, either using alter partition.. . move or alter table ...move, for which you will have to have some period of no access (only in 8.1.6 and above other wise no access for whole process at all) during the start and end of the process.