PERSONAL LOAN SINCE 2005. HELP PO PLS

I need an advice also please po. Someone from SP Madrid has been continuously calling and asking me to settle a loan na way back in 2005 pa. I honestly do not remember if I have paid in full pero I am assuming that I have kse ang last payment ko daw is 2008. First time nila tumawag sa kin. SP Madrid asked for my email address. I gave it na lang kse kung saan saan na sila tumatawag sa kin. Sinabi ko din sa kausap ko, pag ako nawalan ng work, lalo akong di makakabayad sa sinasabi nilang utang ko. I told them to stop calling me. Yesterday, SP Madrid sent me a bill via email, nakalagay dun na ang outstanding balance ko is 38K+ tapos ang total amount due is 478K dahil sa interest, penalties and atty fees. Binigyan pa ako ng amnesty program and kelangan ko masettle on or before the 13th of this month. I don't know what to do now. I have just started working and I am so broke. Kahit magkano wala pa akong naipon kse kakastart ko lang.
Is it wise to respond to the email of SP Madrid para sabihin na di ko kaya bayaran ang hinihingi nila at hingin ko sa kanila ang proof of payment ko? I don't know what to do. Please help me.

Humingi ka ng proof kung saan kamo nagstem yung utang mo. until you have this and have yet to confirmed na may liabilities ka talaga, you can tell them to stop contacting you.

Maraming Salamat po, Atty. Susundin ko po ang advice nyo po.