You are one of the most unfortunate owners of an ATI GPU, which is an awful
gpu for it requires nonfree firmware to work correctly. The libre kernel
Jxself packages should at least give you the correct (native) resolution.
Make sure you install and use (select in GRUB) the **latest** kernel (4.8) as
on jxself's website.
https://jxself.org/linux-libre/
The real solution would be for you to sell your current laptop and buy one
with an Intel gpu (just not the latest one, skyblob skylake). Without video
acceleration those ATI gpus are useless crap :(