What i do, and you can do that in any country i belive is this.
Go to the operator that you dont use.
buy 5-6-10 as much is the limit of simcard you can have on your name.
Chek what is the minimal and maxium amount of credit you can send to another prepaid card.
(In my case card comes with 1E on it, but you can send minimum of 2, in that case manually top up until you have minmum)
after opening account, verifying it, whatever,
take second sim card, make an account, do your thing and than send credit from SIM1 to SIM2
after finishing with SIM2, do the same to SIM3
at the end you are gonna end up with one-two-three sim card (depending what is maximum you can send of credit) topped up with 20-30-40E
and this is operator that you dont use and assuming you have normal sim card with a plan that is post-paid in order to do recover some of this cost i do following:
1. find some friends who are on that network and are pre-paid users and ask them to pay you to transfer them credit insted of topping up. For them is the same, sometimes even more convenient.
2. keep this in spare phone and use it to pay parking or some sort of that service that you pay via phone anyhow.
3. give it your mom to call her cousin in Australia and spend all the money on roaming
Don't forget to organize simcards nicely, always turn of PIN or make sure to change generic one to something like 1111 that you will always remember.
Chek with network what is minimum you need to top up per year or 6 month period in order to keep them active and operator doesnt turn them off so you can have them in case instagram ever needs to verify again.
At the end if you don't end up using them so much, you can easily offer this service to someone for 10-15-20c depending where you are from and if they are running an account on proxy from your country, this could be usefully.
just my 2cents. Cheers