I have a feeling what I didn’t think worked to cover entire transactions might have only applied to Play Store credits earned. If you have an actual $ balance on the account, then I think it should work like your situation. Credits do expire, but I wonder about the balances though, and if they do, ouch.
I haven’t been a true F2P in the purest form for a long time already, since I spent some promo credit that Google gave me in the past for gem purchases. Again, not my money, but all the same to SGG, it is still incoming $ flow from this account, no matter the amount (or the source for that matter).
You took surveys that you didn’t otherwise have to spend the time to take to build up trickles of money flowing into your balance. I mean, once you built up this balance, it is yours to do as you please, if you don’t play other games or mobile apps you spend this balance on, where else are you going to spend them, I mean, did you not do the surveys in the hopes of one day being able to use it in-game when a right deal comes along? Again, it’s not actual $ out of your bank account, but rather an investment of your time (time is also money, of course).
I would not be too harsh on yourself, my friend.