Ford Focus just had timing belt replaced now garage can't find a solution to car overheating when goes above 20 miles per hour

1. This timing is not right get the timing adjusted with a timing gun
2. see the radiator fan does it work when the engine is hot
3. see the fan if its throughing the air from outside towards the engine by putting a piece of cloth infront of the radiator if the radiator pulls the cloth the fan is in right direction if not ask the garage to fix it

Hi.

First thing to check is the cooling system itself. Check if fans are coming on. If there is no fan coming on, then there may be a defective thermostat.
Check the water pressure. The water pump may also be responsible for the problem.
This is the most obvious stuff, I guess the mechanic has already checked all this.

Bleed coolant liquid. Air pockets in the lines can commonly cause overheating.

After the fan and cooling system, first ting to check is compression. There may be a problem with the head gasket, and this will result in engine overheating. A compression test done on all cylinder will reveal if there is such problem.

You may have an air pocket in the cooling system. Im not trying to bad mouth your garage but did they put all the hoses in the proper location? Did the change the wtr pump and thermostat when they did the timing belt?