My credit score is low?

My credit score is about 300 and barclays declined me for a debit card even if the agency i am working with pays about 2000pounds in my barclays cash card account that i have for 7 months with them.i tried to open a bussines account as i need it because i am self employed and want to start my own business and to take some people to work for me.but i still got declined.they suggested me to apply for a starter credit card and said that can build my credit score.but i was declined for this as well.i wanted to get a contract phone from 3 but was declined.the only thing i could get is a data card form 3 for which i paid 150 deposit and 30pound monthly thereafter.does this datacard on contract form 3 will help to build up my credit score and if so for how much and how long does it take.thanks
Answer
Shop around with other banks so see if any of them will give you a debit card, include the on-line banks normally there are more relax. once the debt card arrives it will be easy to get a credit card which increase your credit score. it may be good for you to see a financial adviser there are will give you free advise.