that hub is fine... what i would do if i was you is to put the cog into a english bb tapper to be sure the threads in that cog are fine prior to install it... the cog must get in there just like butter... the guys in a lbs can do it, it will take like 10 mins... usually cogs have a super rough thread and must be passed again in a tapper. EAI cogs or almost any cheap cog have the problem... some shimano's and some campy's also... Some of them not all.

If you dont have a tapper or an lbs use a super old hub and put the hub in there untill it fits like with butter then put it back in that nice hub u want to use. I bet you dont want to damage the hub again... wonder how u can screw up the last threads of the lock ring... probably the guy put the wrong lock ring in there... This is an old trick I learned like 30 years ago and I have never stripped a single hub ever. Usually people just put the cog in there and it fits super tight, in a matter or fact the fit in general is too tight. is the right thread but tight... U can strip the darn hub, besides the steel in a cog is too had for the hubs threads. So take the cog to the shop and tell the guy to use the english bb tapper in that thing untill it fits perfect in the tapper (5 or 15 mins max) then put it back to the hub...

Good luck.