Cancel the 4G contract and get a new one on a 30 day contract until its sorted. I looked last year and Three had 30-day contracts with unlimited data 4G/5G BB for £25/month.
Smarty (see below) do it for £20 - would need a Mifi or SIM router though

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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.