Over heating is caused by coolant escaping or the fan not working. If your car has just been repaired after a cam belt failure they would have had to strip the engine right down to replace damaged valves pistons etc and to do so would have involved removal of the head etc. Was this a reputable garage? Did they replace the head gasket? A duff head gasket is a common cause of over heating but also check the obvious.
- Fan working? Belt Tightened
- Rad topped up, not leaking?
- All hoses secure, not leaking
Take off the oil cap and look at the oil, is there any evidence of a sort of creamy substance, like mayonaise? if so head gasket is gone, ask the garage if they replaced it when they fixed the engine, check your bill and parts list. If they replaced it and you have mayo then the head is warped, needs skimming, new gasket etc.