Yeah, they're good w/ customer service. But you're lucky you had no line - I've been to various TPH in Sevilla, Barcelona & Madrid & the lines have been massive everywhere.
So, for your questions, let's go to their SIM card conditions, provided on their site:
"El cargo en concepto de Consumo MÃ*nimo Obligatorio se efectuará a mes vencido, el primer dÃ*a hábil de cada mes. Si, en el momento de efectuarse el cargo, el saldo
disponible del Cliente no es suficiente para cubrir el importe del Consumo MÃ*nimo Obligatorio, YOIGO detraerá de su Cuenta únicamente el saldo que esté disponible."
So, approximately: "The Minimum Obligatory Consumption charge will be drawn after the month is over, the first working day of each month. If, upon the moment of withdrawing the charge, your available credit is not sufficient to cover the MOC, Yoigo will withdraw from your account only the credit which is available.
"En caso de que el consumo efectuado por el Cliente durante un mes natural sea inferior al Consumo MÃ*nimo Obligatorio, YOIGO detraerá de su Cuenta
la diferencia entre el consumo efectivamente realizado y el importe del Consumo MÃ*nimo Obligatorio. Asimismo, el importe Ã*ntegro del Consumo MÃ*nimo Obligatorio
será cargado en la Cuenta del Cliente en caso de que éste no haya efectuado consumo alguno durante un mes natural."
"In cases in which the minimum consumption used by the client during a month is less than the MOC, Yoigo will withdraw from your account the difference between the actual consumption and teh MOC. At the same time, the withdrawal will be charged in cases in which the client has not consumed any credit during the month." So yes, they'll be deducting from your account. In another section it says if you stop using the card for over 6 months Yoigo'll desactivate. I don't however, see anything about MOC withdrawals on accounts w/ no credit upon recharge. All translations provided are my own. You can see the document at:
http://www.yoigo.com/pdf/condiciones_tarjeta.pdf