You said, you formated the partition you boot Debian from and then put the Manjaro boot files there? Is that correct? If it is, then you overwrote your Debian system with the boot files for Manjaro. There is probably no making that Debian install bootable again..!
The reason it hangs when you try to boot Debian, is that Debian is nolonger there. The grub entry is there, because that should be on sda1. However the boot files for Manjaro now reside on sda2 where Debian was, so the system stops.
Grub should be instaled on the same partition as the previous grub, and the OS should be installed with the install alongside option.
The boot files should be on the root partition of it own OS or a partition not occupied by any other OS that you intend to use.
The only option I can see from the information provided, is to use a data recovery tool to recover what you can from that partition, as the format and relatively small overwrite by the boot files most likely did not destroy all that much data. You might walk away from this with all the files you need, and a good lesson learned. These things happen, that is why the tools to fix them exist, we are all human after all.