New Immigrant with Bad Credit Issues

Hello People,

I need some advise, I really don't know what to do. So any advise will be appreciated.

I came to Canada on a student visa and stayed here for 2 years during this time I had a SIN no starting from 9. I also had credit cards from TD, MBNA, RBC, Zellers, Futureshop, and an over draft from TD. 

I filed my PR and went back to my home country as my visa expired. I was in my country for 2 years and now I have received my PR and I am back..

The most foolish thing I did was I stopped paying my bills when I left the country, another reason I did that was I was out of money.

 I also had a FIDO contract and a rental lease

Now I am back not only with Bad credit but also with no clue whom should I call to make the payments as no collection agency has my no or my address.

On my credit report it says "bad debts" against all cards and accounts.

So I have 3 main questions, 

1. what is the best way to pay off these debts, and how should I go about it.

2. Once I pay my debt to the collection agency what effect does that have on my credit history. I mean the banks have already written it as bad debts.

3. What's are the Do's and Don'ts in my case, that any one can recommend.

I am trying to settle in this new country with an extremely bad credit. :(