We won't visit drug addict son in prison - from parents of prisoner

Dear PWUK. Our son is in prison in the UK and this is his third prison sentence. We have supported him but this time around we have refused to visit him. Enough is enough and me and my husband are NOT sending him anymore money because the money we have sent him previously was spent on drugs in prison. It is all well and good that families are encouraged to support their loved ones in prison but there is a difference between supporting a loved one and enabling them. Our son was constantly ringing us both off a prison phone and mobile phones asking for money. He was phoning us off mobiles through the night and early hours of the morning begging for money. We had been through hell and back with his demands for money, for drugs, before he was sent to prison and when he did get sent to prison the demands were worse! We have had to pay for our landline number to be changed because we cannot cope anymore. Any parent or partner of someone with a substance misuse addiction will understand that there comes a point when enough is enough. You can't fix a drug addict no matter how much support you lay on the table. My husband and I have always said to him that if and when he decides to fight his addiction, we will stand by him. Whilst he is in active addiction, the parents cash machine has now stopped working and we are no longer visiting him and taking his phone calls. 
It is like banging your head against a brick wall. We were told, oh you really should visit him because this might make him depressed and may result in him using more drugs in prison. But where's our support here? We were being telephoned by him and other prisoners in fact badgering us to send money and it was making both my husband and I ill. Where is the support for families when the prison's can't get their act together? Sorry no, if you have walked in our shoes then sure you can bleat off at us, and yes this has been a tough decision but for the sake of our own sanity and health, we have had to walk away and stop feeding our sons drug addiction. Please publish as Anonymous. Thanks.