credit score gone down from getting a credit card ???

i am looking to get a morgage in the next 6 months.
unfornatly looking at my credit score i have an un paid phone bill (which i have sorted now) and not on electro roll (will be on in december) my score isnt great from these two things but i have always paid phont/car/subscriptions from my bank and apart from that phone bill and a breife stuggle when i was 17 (the insurnace made me overdrawn by a couple of quid)i have been very good. I stuggled to get a bank card and im even more !!!!ed off that barlcyes promised to soft check me and done a hard check that also dented my score. but one thing thats coming up as a negitive now is that i have a credit card and also its bad thats ita only £500. i have been buying fule (aprox 60 month) off it (i have only had the thing for 2 weeks so yet to see if it dose me good) but my question is is how do i get more money? and any tips for using it to get my credit score back up fast.