As @Yonggoo Noh said,
확실치 is equal to 확실하지.
확실친 is a short expression of 확실치는 or 확실하지는.
확실하지는 has the same meaning as 확실하지, but those have a slight different shade of meaning.
Let me explain more detail.
Generally, -하지 is shortened to -지 or -치.
(But -지 is not a short expression of -하지 since there is an exception like 먹지 않다)
It is determined by whether -하지 follows a voiced consonant(울림소리, including ㄴ,ㄹ,ㅁ,ㅇ) or a voiceless consonant(안울림소리, the rest of consonants).
확실 ends with the voiced consonant ㄹ. So 확실하지 can become 확실치.
On the other hand, 넉넉하지 cannot become 넉넉치 but become 넉넉지 since 넉넉 ends with the voiceless consonant ㄱ.
Similarly, 충분하지 becomes 충분치 and 섭섭하지 becomes 섭섭지.
For 확실하지 않다 and 확실하지는 않다, themselves have the same meaning. However, 확실하지는 않다 involves slightly doubtful feeling and may leave room for saying more. So if someone says 확실하지는 않다, then you may expect he or she will say something could be 확실.