Credit Question

So as soon as I turned 18 I made a huge mistake which all in all is a lesson that I am now learning from. I decided to get the newest iPhone and finance it. I also opened 3 lines of credit over the course of that year. I’ve paid off my two of my credit cards which had $500 balances on each of them. Now back to the stupid phone. I ended up getting that phone stolen at a party. I stopped paying the bill and now there’s an $1,000 balance that was sent to collections since Verizon closed my account. My question is should I pay that in full like I did my two credit cards? Will that help my credit even tho the account is closed? Same goes for the third credit card the account is closed with only a $300 balance on it. Would paying those off in full right no help me? Also any tips on raising my embarrassing credit score? I plan on scheduling a consultation with a credit repair specialist.