Recharge prepaid sim cards automatically


I`ve been searching for a long time how to recharge automatically the sim cards of mobile phones.

Recharge prepaid sim cards automatically by dialing a number.
We have a gsm gateway, I connect to a MERA switch in h323 with ephony (h323 softphone) and have to recharge a lot of sims.

I installed a server with asterisk and freepbx, create a sip user on the MERA and I can now make the calls and recharge the sims one by one on SIP Protocol. like this

234121299 (prefix) + 12 (number of the channel) + 555 (number to call for recharge) then opcion 3 then XXXXXXXXXX (recharge pin code)

The thing is that I want to recharge 10 or more sims at the same time.
My head is no working anymore, I`ve search for posible solutions and find nothing…

For example I want to recharge channels 12, 44, 23, etc… same time

Someone can give me an idea on how to do this?