Blue label connect is a ****

I took out a contract with Blue label connect... Worst mistake in my life. Firstly the 1st year no airtime was loaded whilst I made monthly payments. The fone only worked 3 months, they fetched it to fix it and brought back a different handset... Which also broke after a few months. My contract ended end of March but now after checking my credit score I find that Im owing Blue label connect. This is affecting my credit... This needs to be fixed asap... Blue label connect are *****s