It seems highly unlikely any ISP will refuse to take an order and your money if they are capable of giving you the service. I mean, think about it. What exactly would Vodafone have to gain by telling you that they are at capacity when they aren't?
If it's a physical lack of ports to plug you into or a bandwidth capacity issue - sounds like the best thing was to cancel your order rather than show-horn you in.
No ISP is going to refuse to take your money if the other option is take it.
I couldn't be bothered to post the full backstory as to why I doubt this explanation originally.
In short: been trying to switch ISPs since May. Tried moving to BT they put through 8-10 orders all auto-magically cancelled and they have no idea why. Have previously switched over the years without issue from Sky to BT, then BT to Plusnet. Escalated to Openreach confirmed no stop/cease on my line, no issue with local exchange or cab plenty of capacity and ports. Despite already on a live fibre service anyway, there was no reason. In the end BT give up, gave me £50 to say sorry and told me to try another provider.
So I went to Vodafone - again tried 3 orders with them and all cancelled. 1st time was told cabinet full but would retry order. 2nd order failed the agent claimed there was no capacity issue or why they originally said this, so would redo the order. 3rd order failed and went back to original story, sorry no available ports for us.
Ironically the executive complaints handler at Plusnet stated it was a known Openreach fault on some takeover line orders. The solution was to ask the new ISP to place a broadband transfer only, followed by a line transfer 2 weeks after. Vodafone were so inept they believe can only place full transfers, all or nothing! So I give up.
Now do you see why I was very dubious that 'cab is full'? I know it's tosh as well as I'm on a new estate and we even had a 2nd huge fibre cab fitted, I know there is plenty of capacity even OR confirmed. So, hence I give up and stuck with Plusnet and renewed my contract. I've spent 3-4 months trying to switch ISP and it was draining, I was wasting so many hours each week on the phone, debating the toss and logic behind the order cancelling. No one had a clue not even Openreach.