My exact experience too!
In fact my wife and I were talking to the owner of a
dealership last night and this topic came up. He was recommending a Scotshield warranty on the used car we're looking at rather than the Seat warranty. He said that you tell Scotshield about the fault and they just pay up. You tell Seat about the fault and they try to deny it. You end up arguing with them and struggling to get them to pay for things that are clearly covered.
This correlates with my experience when our current car was still under the original manufacturers warranty. Being told things are not covered when they are on the list of things that are. Being told that it's not a known fault or they can't find it when it's all over the internet.
Clearly, Seat are just tightwads. I think you have to accept this going in. The cars themselves might be good but the bean counters at Seat just want your money. The sat-nav updates are a good example. Not only do they charge you a lot for what other manufacturers give you free but, even when you do buy a card, it's out of date because Seat don't want to pay for the maps.
Buyer beware.