I had bought the pre-paid service package for the 1st 3 years, and I just noticed that the last 2 oil changes done by the dealeer was with 5/30 oil.

Previously they used either 0/20 or 5/20...

They said the 5/20 will work just fine... and I haven't had any problems, but
they also mentioned that the 0/20 and 5/20 oils cost more...

 

My engine oil cap specifically calls for 0W20 or 5W20. If you purchased the service package they should be using what is designated on the oil cap at no extra cost to you. They are "supposed" to know what is specified for your vehicle and if they didn't take that into account when you purchased the package they eat the difference, too bad for them. I would be having a discussion with them about that. I don't trust dealers on anything.