DEC is diethylcarbamazine. It is largely ineffective against flukes. Flukes are trematodes, which are most effectively treated by praziquantel (PZQ), and to a lesser degree of effectiveness nitazoxanide (brand name is Alina don't know what ir if it even has a common three letter abbreviation like most dewormer meds). However liver flukes (fasciola hepatica and related species) are mostly immune/resistant to PZQ and require triclabendazole instead, which is mostly ineffective against other types of flukes.
Are you sure it's flukes you have? And not maybe some type of large Ascaris (nematodes/roundworms) which can appear as big fluke-looking chunks when passed in stool. DEC can be effective for several types of ascarids.