tourist visa gives you 60 days in the country. Which you can extend by 30 days. The exempt entry with no visa also gives you 60 days which you can extend for extra 30 days at local immigration.
90 day visa is the validity period to use it to enter Thailand. Then once you land you will be given 60 days stay in the country. If you have a passport from one of the eligible countries you could enter exempt of a visa for 60 days.
You need to answer the question about the ED visa and if it was an extension, did you go to immigration and cancel it. People can't help if you don't answer
The answer from the embassy was correct. The visa ( it is the document allows you to enter thailand ) is valid for 3 months for you to use it. A Tourist visa then allows you to be stamped in for 60 days. You can extend that by 30 days.