Items in the lower refrigerator compartment arefreezing

Your thermostat should control it.

if the flap was open then truely excessive cold air is coming out/escape from the freezer causing no freezeing. you need to defrost your fridge.

Note also that frost build up increases time to freeze your food on the freezer. it also causes your fridge an increase in electricity consumption.

defrost your fridge for some time ti remove the frost build-up.

reasons include ( most probable) a failed thermostat
next is the dial setting has been inadvertantly changed to a lower number

First, check to see if the airflow is blocked at the back of the fridge compartment as this also may cause the lower items to freeze. Fridge freezing is usually the malfunction of the damper swing door or the circuit controlling it. A failure of the temperature sensor in the fridge could be the cause. We just had ours replaced this year [on extended warranty]

Don't think it's the temp control problem, I suspect one on the defrost elements at the top is faulty, if food starting to defrost in the cycle indicates the lower element is working overtime.

Make sure that the fin tubes on the back are not loaded with dust, clean off and don't over load the freezer section. If there is no room for air flow the temperature will keep getting colder to compensate for low air circulation, thus freezing items in the lower section.

the fridge temp is set way to low,set it to about +4C,or adust it so that lettuce doesnt go limp.....

your evaporator coil in the rear area behind the panel is iced up and blocking fan air flow to the freezer compartment

Look all the way to the rear of the control console in the fresh food compartment. Look up into the opening with a mirror. There should be a styrofoam diffuser (61005543) visible. If this is missing or damaged (many people think it packing material and remove it) it needs to be replaced. It spreads the air out rather than let it go right down the back wall to the crisper area.
One other thing to check is a tiny slot at the right rear of the same control console. a metered flow of air comes out the slot to the barrel shaped cylinder with the cold control capillary wrapped around it. Sometimes the slot gets water in it and freezes over. The unit will run too long and the cold air will settle during the off cycle and freeze items at the bottom. More often than not, when the slot freezes over, other items in the fresh food compartment will freeze......not just the bottom items.

check your door not closing stay (ajar)