If you bought the wrong membership by accident and the membership has already started then you just have to wait until the month is up and then buy the correct one next time.
If the membership hasn't started then contact 48 support and they may be able to refund the incorrectly purchased membership and you can then buy the correct one.
http://www.48months.ie/help#ask-a-48-agent
To avoid this hassle maybe you should consider choosing the membership you want and then enabling auto membership renewal?
Automatic membership renewal
If you are on Mitch by accident instead of Guido then it doesn't make sense that you have no internet as Mitch comes with 15GB of data allowance compared to Guido's 1GB!
Hope this helps.
