IPHONE BATTERY REPLACEMENT

Had a new battery replaced in my Iphone 6s less than 7 months ago at Canal Walk Wefix - in the past 2 weeks it's ability to hold charge has deminished to about 4 hours. I paid R500 for this battery only to be told now, that its out of warranty (6 months) so I need to replace it again!!! They are quite obviously using ******* generics as replacements - BEWARE!!