The fact that you’re getting 30 orders a month is great, but for half to be cancelled is not right.
I’ve been selling on Fiverr for seven years. I’ve completed hundreds of orders and I’ve only ever had 5 cancellations - less than one cancellation every year.
All my cancellations were because the buyers assumed I offered a service, such as writing, when I don’t. I didn’t do any work on the cancelled orders.
I’ve had a quick look at your profile. All looks good.
So it’s fair to conclude that the quality of work you’re delivering isn’t to the standard your buyers are expecting.
While your gigs look good, if the quality of work doesn’t match - then you’re going to have some annoyed buyers.