Communication is always a key factor in whom you hire for freelancing work. Communication is 80% of the job.

If he/she hasn't responded in weeks, then he/she most likely isn't doing his/her job or he/she ended up sick and in a hospital or something.

Some freelancers don't understand the specs or instructions, as many are ESL speakers, you may have to communicate in their native language if English is a bit of a roadblock to them understanding what you want them to do.

You really need to go over the contract this freelancer signed with you, and see what it says about not fulfilling his/her end of the agreement. Stuff like no communication in two weeks should invoke a clause that the freelancer has quit the job and forfeits the pay that the/she would have been paid for those two weeks, and breaks the contract.