Add salt light still flashing after adding salt

Hi, I have a salt pool 10 yrs old with an autopilot pool pilot soft touch system. The add salt light started flashing towards the end of winter. When I check the salt on the system it reads 300ppm. I added 2 bags of salt and still had a 300ppm reading. I took a sample to my pool store and had it tested and it read 1800ppm. I bought the 4 recommended bags of salt and have added them to my pool. I am still getting a 300ppm reading on the system itself, after adding 6 bags of salt. I replaced the salt cell last season when no chlorine was being produced. It did nothing when I replaced it for the chlorine at first, and then stared working later. So I am thinkin the cell wasn't the issue, something else may have been going out. I don't know if it may be the tri sensor or what. I took the tri sensor off and looked at it and didn't see anything out of the way, but I am not sure what to be looking for. Also when adjusting my output settings the output never flashes to signal sanitizer or purification mode. I am guessing the system not reading any salt causes this. If anyone has any ideas, I would be very greatful.

Thanks!