lack of appropriate responses

i recently settled all my accounts with my creditors, while my credit score has increased with the respective credit bureaus it has gone down with Transunion. subsequently i am unable to attain new knew in order to build a healthy credit score. I called in to their disputes and customer services (reports) department respectively hoping someone would be able to assist me with my concerns.

I called the disputes department and they advised me that they wont be able to assist me because i am speaking with the wrong department. I recently paid of An FNB account which had a legal status as as far as i know when you settle an account that was in arrears your credit score needs to increase but in my case it didnt, I then with the hope of wanting to build a credit score app**** for a store card which was declined because of a low credit score. I spoke to a lady by the name of terry whom i explained the situation, but felt as though we were just going back and forth and not coming to a conclusion , she then decided that she would stop taking to me, and i went on speaking by myself for about a minute and half realizing that she was no longer responding hang up. If your company can see when i have app**** for credit then reduce my score for doing that why then not increase my score when i am making payments regularly to a point of settling the accounts that were handed over?????

Please advise why my credit score has reduced instead of going up.... and how can i apply for credit and build a healthy credit score if creditors are refusing to grant me credit because of the information Transunion has about me.