Does a Top up voucher code expire?

Hi all.. Ive got 2 top up voucher codes that did not work when i trued topping up after a week of purchasing the voucher from a local shop...
So the question is.... Does the voucher number ever expire and if so what is the time sensitivity on that please?
It was actually a friend of mine that buys them for me BUT i had already got credit and i thought i would save it for when i needed it next.
When i tried doing the top up by voucher i thought perhaps the number he had txt me was incorrect BUT alas it wasnt.
I am a busy person and i just ended up leaving it ...but i was going through my phone and i saw these txts with the voucher lebara numbers etc and this promoted me to ask you, the public and of course Lebara themselves to help shed light on the matter.
Thanks in advance...
Gemz

No188 to answer the first part of your question, yes top up vouchers do expire. This is referenced in the Terms and Conditions. There are several reasons including fraud prevention, network resourse management and to comply with prepaid telecommunication terms.