If they don’t respond then be sure to complete the work exactly as they said in the order and in-line with any portfolio you have and submit finished, being sure to use the formal job Delivery box, within time allocated for the job.
It is then on the buyer to accept the work. Depending on what your gig says with regards to revision*, they may request changes. If they request changes based on new info you may/should request a further fee as that is not a revision but a rework.
If they try to cancel, decline the cancellation. If they get aggressive and/or make threats, esp about reviews, refer to CS immediately and wait.
*I do hope you didn’t stupidly write endless revisions or similar about working until customers are happy as if so you will probably lose every fight. If so look to cancel or get out of the job as soon as they get narky and fix your Gig to read more professionally.