If you are watching Freeview then the signal gets to your TV via a standard TV aerial. It won't have anything to do with satellites or dishes.
And if you are watching Freesat then the signal gets to your TV via a satellite dish. It won't have anything to do with TV aerials.
This losing channels thing is pretty common where the receiver box or TV has only a limited amount of storage space for channels. If you have done a factory reset and made sure the TVs firmware is up-to-date then there are a couple of extra things you can try...
1) Delete some of the channels that you never watch. This will free up some memory slots.
2) If you are still losing channels even after deleting 4 or more unused ones then you could try a manually tuning each MUX for your area, then deleting any unwanted channels in that MUX before moving to the next one. But unless you know what a MUX is then that's about as clear as mud. lol If you are unsure then this might help.
On the old analogue system we had 4 or 5 TV stations depending if we could pick up channel FIVE. For tuning purposes each of those stations had a channel number. My local transmitter is Winter Hill. So on the old analogue system BBC1 was broadcast on Ch55, BBC2=ch62 ITV1=ch59 CH4=65 FIVE=48.
Digital uses channel numbers too, but instead of being one station per channel number there are now a group of stations. This is what we call a MUX. The MUXes for Winter Hill are MUX1=ch56 MUX2=ch66 MUXA=ch68 MUXB=ch67 MUXC=ch60 MUXD=ch63 MEN=ch57. To see what's on those channels have a look
here and scroll down. You can use the site to check your local transmitter and the channel numbers.
So, fixing your problem...Find the channel numbers for your local transmitter. Do a manual tune one MUX channel at a time. Once the channels for that MUX are downloaded go back to the tuning menu and delete the channels you don't need. Once you have done that move on to tuning the next MUX and repeat the process.
Thinning out the TV channels like this is the last stop before calling it quits with the TV and replacing it.
Let us know how you get on