First of all contact the baliff's office and try and speak to a manager, explaining the whole situation. If you get no joy say that you will report the incident to the police as the bailiffs behaviour could be charged as threatning behaviour, for intimidating your son and calling you names. This can also be charged as slander, or other similar charges.
They cant just dissapear for 6 months then turn up, they have to be sending you regular letters or contact of some sort letting you know the situation. You can sue them for harrassment if they continue.
If he comes back ay you have contacted the police, and you should. Pay your debt, and as far as you being a guarantee for someone im not sure how this works, you ned to seek legal advice to see how you can get out of that situation.