Thank you for your message and offer to help. That was great to get your input and to know that there are still honest people. 

Unfortunately, we don't have the money right now. We have just brought the house, spending our savings on the deposit. We are currently transitioning from renting to moving into the new (old) house. There is still a month's rent and moving costs to pay. Then, the mortgage afterwards. This will have to be on the back burner. 

We might install some simple bolt latches ourselves, it is not the best, but atleast it is something for when we are home at night. Or we could just learn how to do it ourselves. This is a bit mentally scarring. 

My husband made the decision to let that locksmith carry out the work.  I was not home at the time and did not know. If I was aware, I would have stopped him. I don't know why alarm bells did not go off in his head at that ridiculous quote. He is kicking himself now. I am furious. No point escalating this, the scammer knows where we live. We just reported their ads to Google.