I never contact you out of the blue.
I'm sorry for not contacting you for so long.
I am sorry for hardly contacting you.
Please don't contact me anymore.
I am sorry about contacting you late.
I'm sorry I haven't been able to keep in touch with you recently.
There is something that I want to talk with you about so I contacted you.
I am terribly sorry about contacting you late.
I am terribly sorry about contacting you late.
I am terribly sorry about contacting you late.
I was worried because I didn't hear from you.
I'm sorry I haven't really been able to keep in touch.
I am terribly sorry for contacting you late.
I am terribly sorry for contacting you late.
I am terribly sorry to contact you late.
I'm sorry for contacting you late.
I am sorry I was out when you called
I am sorry that I couldn't contact you yesterday.
I am sorry that I couldn't manage to contact you.
I'm terribly sorry for contacting you so late.
I am sorry that I didn't contact you.
I feel relieved that you got in touch with me.