iterate of automorphism cannot diverge on compact sets, but

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Let $\Delta\subset\mathbb{C}$ be the unit disk and take $f:\Delta\rightarrow \Delta$, defined by $$f(z):=\dfrac{2z+1}{z+2}.$$ It is known that $f\in Aut(\Delta)$, since we can write $$f(z)=\dfrac{z-\alpha}{1-\bar{\alpha}z},$$

with $\alpha=-\frac{1}{2}$. Hence, the behaviour of the sequence of the iterates $\{f^{\circ n}\}_n$ of $f$ is at least pseudoperiodic and $f$ cannot diverge on compact sets.
But, we can explicit the $n-$ element of the sequence as $$f^{\circ n}(z)=\dfrac{a_n(z+1)+z}{a_n(z+1)+1},$$ where $a_n$ is defined by $a_1=1$ and $a_n=3a_{n-1}+1$, so in particular we have $$\lim_{n\uparrow\infty}a_n=+\infty.$$ Thus what it seems to be incompatible with $f\in Aut(\Delta)$ is that $$\lim_{n\uparrow\infty}f^{\circ n}(z)=1\qquad\forall z\in\Delta,$$ or in other words that $1$ is the Wolff point of $f$ and $\{f^{\circ n}\}_n$ diverges on any compact subset of $\Delta$.
Where am I wrong? Thank you.