Yes, it could the sales people stretching the truth a bit. Giff Gaff and others rely on PAYG just as much as contracts. My late husband's Vodafone sim is still usable after all this time, with about £5.50 left on it
I've also got 2 straightforward phone sims that don't expire (without data, so just for calls) from different companies than my normal one. I keep them in spare phones to hedge my bets because I'd hate to be stuck somewhere without a signal. There's been no world from them either about stopping the service. Fingers crossed it's not true.