Customer Service help

I have been running an electronic repair business for almost a year now. I am not sure if other businesses in the same field have the same problem. Customers seem to bug us often for their device. I will tell a customer that their devices will be done on Friday because I have tone wait for paresponding and they are contacting me the next day using various communication channels. And they do not stop. I had one person contact me via yelp, Facebook, email and call me 8 times to see if it was done yet. I got other customers who seem to think they are telling me what they are paying for and what they are not. It is just stuff like that.

I am not sure the best way to stop this and or communicate that I will let them know when it is done