Reversed transaction

My son D J Potgieter transfered R5000 into my account on 31.01.2016. I then paid my rent on the same day. Yesterday they reversed my transaction claiming that said money was not available in his account. Now they are taking any monies paid into my account. There responce is I used money that was not mine. My point is that according to my records I did have the money. There claim is I should have confirmed with him whether said money was taken off his account. Who contacts a person paying money into your account whether the transaction went through on their account. Why was transaction only done 17 days later. I am a pensioner with no income and rely on support from my children. In one day R700 was taken as it came in. They claim I owe them R4282. I feel this correction should have been sorted out with Mr Potgieter as he was the one that sent the money to me and according to them did not have the funds. Further more how can Capitec allow this transfer if there was no funds available. When contacting their call centre was told I used money that was not mine and nothing they can do I am responsible. It is all unfair and processed incorrectly.