Frustrated by inability to rebuild credit.

So as the thread title goes I'm at my wits end with trying to repair my credit rating.

A littl bit of history, i got myself into abit of debt when i was younger(Catalogs for my mom and sister) The former of whom have passed away. I moved out when i was 19 and never had the heart to press my mom for the cash for them due to her being short of money. I stupidly turned a blind eye but when she passed away last september a few days before my 27th birthday i decided to get my act together and sort my life out. I found out that i owed about 2k, I paid it off over the next few months and kept an eye on my credit score. It's currently at 576 with a rating of poor, I used experians search tool for help and had a 90% chance to be accepted for a credit building card. I applied and was turned down.
The following month my credit score stayed the same but I'd registered to the electoral roll and finished off the last of my repayments in the month between and nothing had improved, i was given an 90% chance for a vanquis card, was turned down but offered a chromatic card with them but when i tried to accept it kept saying Error and loading a white screen.

I want to own my own house by my 30s and i don't struggle for money but I'm really not sure what to do at this point?

Any tips or help?

Regards, Tom.