Hard to know without knowing what exactly you've actually done, but from the SEAT Ateca Navi manual, this has always worked for me on my 2017 Ateca.
New destination (enter destination)
● Press the function button New dest. in the navigation main menu.
● Press the function button Options and select the destination data you
wish to enter (Address, POI or On map).
To select an address you must always follow the sequence shown: first the
country, then the town, and so on. For “town”, you can indicate a town or a postcode.
After entering the town, you can start guided navigation to the “town centre”. When narrowing down the destination address, please note that every entry
restricts the available range of subsequent selections. If, for example, the
street sought is not found in the postcode entered previously, it will not be
in the previous option to select the street either.