Sink pipe blockage issue

[Chris1895]

Had the plumber replace the pipes less than 2 month from the sink that lead into a cast iron pipe. They also unblocked gunk from the start of the cast iron pipe.

The gunk is in the photo I've attached. The pipe work is also attached(it's disconnected as we cleared the u bend to clear it out).

Question: Why would we get this blockage so soon after and what could be causing it? Seems like the blockage is possibly further downstream. Any ideas on how to resolve?

 

[cjg]

stop putting fatty stuff down the sink or run lots of HOT water down after,