We have a BIssell cleaner and it works great. We have 3 dogs.
Are you sure you let the carpet dry between all those shampoos? Also, if you use too much soap it makes it worse.
We don't have the issue anymore unless a dog is sick or something but my strategy is... blot up as much as possible with paper towels. Then, i douse with straight vinegar and make sure you douse a spot larger than the pee spot so it goes through to the pad and maybe more.
Then, I soak up the vinegar by using a lot of pressure.
If my cleaner is handy at the moment, I will then use it with HOT WATER ONLY and suck up the excess vinegar.
In the past, I have also used the vinegar and then used a steam iron to get everything up. This works well but it stinks like crazy (the steam/vinegar solution)
In the future, watch the dog closely when he is in that area because they can find an old pee spot with their nose...
Good luck.