Firstly are you running the latest beta version of the TBB? Secondly buying BTC linked to your bank account is not a good idea, think of it this way, you are using Tor to be anonymous on the internet so you can access SR but you are then linking yourself to the crypto currency you are going to use to buy illegal items on the dark web and have them shipped to you. You should acquire your btc anonymously, have you checked out localbitcoins? def worth a look. If you buy your coins in this way there is no need to worry about all the tumblers before transferring to your SR account, you have already broken any link between you and them. Hope that helps, ask away if you need to know more.