This.....and if the OP's former employer finds out, this could affect "references" when applying for a new job.

It might be understandable if the room had been booked before the OP was told of the termination, assuming that the company's policy permits use of their corporate code for personal travel. However, to deliberately book a hotel using a rate code of a former employer would certainly be considered fraud, unless of course the company permits use of the corporate code for personal travel by retirees.