That's the WNROS result you had. Check the yellow box above the map for details of exchange etc.
Are you sure you know for certain which exchange you are on? Use the BT checker below to be sure. Use your phone number if you pay your phone line rental to BT or otherwise use the address check. Don't use the post code checker.
There seems to be an issue either on the BT DSL Checker site or the telecom-tariffs.co.uk site.
Acording the the BT DSL Checker postcode LL28 4DE is connected to Exchange COLWYN BAY CENTRAL (WNCB) cabinet 14, however when you look for that postcode for all the supported postcodes for that exchange postcode LL28 4DE isn't listed on the CodeLook Site.
Strangely on CodeLook postcode LL28 4DE is listed as being supported by Exchange Rhos On Sea (WNROS) and you can see it as being listed in its supported postcode list for that exchange as being on cabinet 12
So I think something isn't right there, and has added to the confusion.
Maybe recently that postcode was moved over to a closer cabinet that was on a different exchange and codelook hasn't updated this yet?