Today i received a reply from support and it answered all my concerns:

The interests are calculated hourly. If the trader closes the position within one hour he will pay one hour interest. Otherwise he will pay interests calculated for each hour the position was opened (up to the next round hour).
Interests are paid every night around 00:00 GMT


So interest for cancelled refunds within the hour is accounted for and credited only at 0:00 GMT.
I 'd like apologized for my tone in previous messages, i was annoyed for getting 50% refunds within the hour, and felt being played seeing my balance staying the same.

@Ente  30 day loans between 0.7% - 0.94 % with half refunded within hours. Maybe its mainly due to yesterday's ending rally and traders closing prematurely their position! Also the ability for borrowers to close a loan anytime and take a new offer at a better rate. While the lender is stuck at his pre-set rate and time..