No income as Self Employed, do I need to pay NI Class 2

Hello, I have been registered as self-employed as a sole trader. Last year I had no income from this, but I was employed in a company (with normal salary, tax deductions and NI contributions) so I received income that way. I went to do my self assessment and typed everywhere £0 for the earnings apart from the places where they asked me to fill in my income as an employee. Now the summary of self assessment is spitting out that I owe £122.00. My questions are: a) why do I owe any money if I did not earn anything through sole trading b) what is this charge? Is this NI class 2? I have paid all due NI through my employment with the company so I don't know why I owe this. c) how do I de-register as self employed? I am not going to be a sole trader anymore and I don't want to keep on filling up self assessment. I tried calling self assessment line and I was on the phone for over an hour, ater which they have hanged up - they are useless. Are any of you kind souls are able to help? Many thanks!

Hi evie1989 evie,
If the charge due is in fact related to class 2, this will show on the calculation roughly 3/4 of the way down as it will specifically say Class2 charge.  
If you no longer meet the criteria for a return please see:- Self Assessment tax returns If you no longer need to send a tax return
Thank you.