Messy divorce is becoming a financial nightmare. How do I get my husband to take responsibility?

I moved myself and my son to the UK in 2003 to get married to a british citizen. I sold my house and all contents in it (wasnt terribly valuable) to move to UK. I was given indefinite leave to remain after our wedding, but no recourse to public funds. My husband didn't have much when we arrived - rubbish flat that was condemned 6 months after i got here, and some dodgy used furniture and appliances. Over the next 4 1/2 years we moved into a much nicer rented house and were able to get nice furniture and new appliances, etc. I have consistently worked two jobs throughout to pull my and my sons weight. Husband decided to leave me in March for a woman half his age. Am not bothered and glad he is gone, much happier without his control freak attitude around me and my son. Problem is this man owes me �4000 for a credit card bill he rang up in my name. He also obtained a mobile phone contract in my name without my knowledge. His excuse - because he couldn't get one with his bad credit. Have tried to reason with that provider to no avail 'because he is my husband'. Me and my son still live in the rented house we shared. Husband has left all furniture, appliances etc for me in the house. He installed a conservatory on the back of the house using a large cash payment he received for an odd job and now insists he should have the conservatory. I actually need that conservatory to sell to recoup the money for that credit card debt. I am wondering what rights I have as far as his agreement with immigration in reference to my marriage visa that says he would make sure me and my son were financially looked after when we moved over here. I would be happy for him to just leave me alone and not give me a penny, but he keeps insisting on trying get that conservatory and not pay me back.