Low Or No Phone Service After Upgrade

I recently replaced two iPhone 4s with two iPhone 6. I purchased two brand-new AT&T nano-sim cards, took the necessary steps needed to deactivate the old micro-sims from the 4s and activate the new nano-sims in the iPhone 6. I then set up the new phones using backups from the old phones. Ever since I made the switch, the AT&T service has been horrible. Both phones show one bar and frequently drops calls. We did not have this issue when using the iPhone 4s. I’ve searched for a solution online, but have yet to find anything that will resolve this. I reset the network settings, still nothing improved. I’ve tried restarting the phones, hard resets, turning Airplane Mode on, then off.....nothing works. No clue if there’s a problem in the service area, but if there is, it started on April 24th, the day I activated the new phones and that’s when the problem started. AT&T service since the phone upgrade and is quite unacceptable, especially given that I pay $150 monthly.

Is this a temporary glitch on the part of AT&T or Apple? I’ve contacted AT&T regarding this as well.....it’s either an AT&T or Apple issue. I’m awaiting their response.

I’d appreciate it if this can be resolved. Please respond.

Frank