How a $1.50 part can cost $2000

The tightness was transmitted from the bolts head to the threads in the block. The bolt head is gone now. Hit the bolt toward the block which reverses any stretch in the threads. You could even hit the bolt inward or down. Outward might crack the timing cover. I have used a air hammer.
Use a small pipe wrench to work the bolt both forward and back. Spray chemicals are helpful. Good luck