Penalty & Enforcement Question

[WGGriffon]

I was working a game last week and a call was made by by our R and enforced over the objection of the BJ and U. Here is the scenario:

A throws an interception at B's 30 yard line. During B's return at A's 40 there is a "block in the back" (as the referee called it) by A. The run ends on A's 19yard line. The R signals a BIB and proceeds to insist that it is a live ball foul and should be spotted at the 9.5 yd line.

I'd love to hear someones feedback.