A surprisingly common issue amongst all smartphone users is that they often do not hold the speaker to their ear for optimum volume delivery. Simply put, they often hold it to their ears incorrectly!
If you have increased the volume to max but still can't hear your calls clearly, it is possible that while you get used to Chatsie's hardware you may not be holding the speaker to your ear most efficiently. This is a particularly common issue with Chatsie phones as they are larger to allow for increased text size for those with visual impairments or short/long sightedness.
That means the larger length of the phone naturally leads people to expect an experience more similar to a landline, where the round speaker is placed towards the top, but not quite at the very top.
The horziontal speaker for a call on a Chatsie phone is right at the very top edge of the phone. People often put the top of the phone to the very top of their ears like they would with a landline, but with a Chatsie phone this means the sound of their call misses their ear canal, bouncing off their upper ear and making voices sound frustratingly quiet or distant.
Next time you are on a call, try placing the top of the phone around halfway down your ear, so the top of the phone is level with your ear canal and the direction of the speaker is perpendicular with it. We've seen huge improvements in our customer's experience with this simple trick - give it a go and see if it helps!