Refuse to release my tablet even though paid

I pawned my tablet for a month in the hope paying back the funds - I then called in to extend the loan repayment period by an additional 10 days(standard practice) we agreed that we would do so I would be charged an additional R86.00 and that I would repay the loan amount on the 27 July 2015. On the 27th July I eft the funds at 23:30, I eft d the funds online and when I went with the proof payment I was told that I must pay an additional R320 in order to release tablet. This firstly very underhand because this is not stipulated in any of the terms and conditions , this infringes on all aspects of treating customers fairly , they are dirty establishment that are running a sham business , trying to hide various gimmicks to it appears that they are hiding behind gimmicks and fictitious reasons in order to attain (*****) pawned appliances in order to sell them at very high markup percentages.