One option is get a 'proper' 4G router fitted with an external 4G antenna. The get the new EE 200Gig a month data sim package; £60pm!
Check the ofcom site for your coverage using an outdoor antenna
https://checker.ofcom.org.uk/mobile-coverage
Not ideal but might your only option.
Note 200gig sounds a lot but one telly doing 2 hours internet TV a night at HD will go through most of that in a month!