I have taken Letter of reference of my current organization from my Supervisor on the company letterhead.
My question to you are
1. I don't report to him directly, would that be an issue
2. This is a small company and letterheads' are easily accessible to Superiors, thus he got a letterhead and issued me a letter, with his contact details on the letter. Would CIC call the landline no. given on the letterhead which could be picked by the head HR or would call my supervisor directly?
No one knows. Seriously, think about it yourself. How can anyone guess which number they would call. You gave them information, they can use it the way they want. Chill out.